or4cl3ai/Aiden_t5
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linux - Running Selenium WebDriver Python bindings in Chrome | I ran into a problem while working with Selenium. For my project, I have to use Chrome. However, I can't connect to that browser after launching it with Selenium. |
You need to make sure the standalone ChromeDriver binary (which is different than the Chrome browser binary) is either in your path or available in the webdriver.chrome.driver environment variable.
see http://code.google.com/p/selenium/wiki/ChromeDriver for full information on how wire things up.
Edit:
Right, seems to be a bug in the Python bindings wrt reading the chromedriver binary from the path or the environment variable. Seems if chromedriver is not in your path you have to pass it in as an argument to the constructor.
import os
from selenium import webdriver
chromedriver = "/Users/adam/Downloads/chromedriver"
os.environ["webdriver.chrome.driver"] = chromedriver
driver = webdriver.Chrome(chromedriver)
driver.get("http://stackoverflow.com")
driver.quit()
| https://stackoverflow.com//questions/8255929/running-selenium-webdriver-python-bindings-in-chrome |
windows - Cross-platform space remaining on volume using python | I need a way to determine the space remaining on a disk volume using python on linux, Windows and OS X. I'm currently parsing the output of the various system calls (df, dir) to accomplish this - is there a better way? |
import ctypes
import os
import platform
import sys
def get_free_space_mb(dirname):
"""Return folder/drive free space (in megabytes)."""
if platform.system() == 'Windows':
free_bytes = ctypes.c_ulonglong(0)
ctypes.windll.kernel32.GetDiskFreeSpaceExW(ctypes.c_wchar_p(dirname), None, None, ctypes.pointer(free_bytes))
return free_bytes.value / 1024 / 1024
else:
st = os.statvfs(dirname)
return st.f_bavail * st.f_frsize / 1024 / 1024
Note that you must pass a directory name for GetDiskFreeSpaceEx() to work
(statvfs() works on both files and directories). You can get a directory name
from a file with os.path.dirname().
Also see the documentation for os.statvfs() and GetDiskFreeSpaceEx.
| https://stackoverflow.com//questions/51658/cross-platform-space-remaining-on-volume-using-python |
linux - Run Python script at startup in Ubuntu | I have a short Python script that needs to run at startup - Ubuntu 13.10. I have tried everything I can think of but can't get it to run. The script: |
Instructions
Copy the python file to /bin:
sudo cp -i /path/to/your_script.py /bin
Add A New Cron Job:
sudo crontab -e
Scroll to the bottom and add the following line (after all the #'s):
@reboot python /bin/your_script.py &
The “&” at the end of the line means the command is run in the background and it won’t stop the system booting up.
Test it:
sudo reboot
Practical example:
Add this file to your Desktop: test_code.py (run it to check that it works for you)
from os.path import expanduser
import datetime
file = open(expanduser("~") + '/Desktop/HERE.txt', 'w')
file.write("It worked!\n" + str(datetime.datetime.now()))
file.close()
Run the following commands:
sudo cp -i ~/Desktop/test_code.py /bin
sudo crontab -e
Add the following line and save it:
@reboot python /bin/test_code.py &
Now reboot your computer and you should find a new file on your Desktop: HERE.txt
| https://stackoverflow.com//questions/24518522/run-python-script-at-startup-in-ubuntu |
Is there a way to figure out what is using a Linux kernel module? | If I load a kernel module and list the loaded modules with lsmod, I can get the "use count" of the module (number of other modules with a reference to the module). Is there a way to figure out what is using a module, though? |
Actually, there seems to be a way to list processes that claim a module/driver - however, I haven't seen it advertised (outside of Linux kernel documentation), so I'll jot down my notes here:
First of all, many thanks for @haggai_e's answer; the pointer to the functions try_module_get and try_module_put as those responsible for managing the use count (refcount) was the key that allowed me to track down the procedure.
Looking further for this online, I somehow stumbled upon the post Linux-Kernel Archive: [PATCH 1/2] tracing: Reduce overhead of module tracepoints; which finally pointed to a facility present in the kernel, known as (I guess) "tracing"; the documentation for this is in the directory Documentation/trace - Linux kernel source tree. In particular, two files explain the tracing facility, events.txt and ftrace.txt.
But, there is also a short "tracing mini-HOWTO" on a running Linux system in /sys/kernel/debug/tracing/README (see also I'm really really tired of people saying that there's no documentation…); note that in the kernel source tree, this file is actually generated by the file kernel/trace/trace.c. I've tested this on Ubuntu natty, and note that since /sys is owned by root, you have to use sudo to read this file, as in sudo cat or
sudo less /sys/kernel/debug/tracing/README
... and that goes for pretty much all other operations under /sys which will be described here.
First of all, here is a simple minimal module/driver code (which I put together from the referred resources), which simply creates a /proc/testmod-sample file node, which returns the string "This is testmod." when it is being read; this is testmod.c:
/*
https://github.com/spotify/linux/blob/master/samples/tracepoints/tracepoint-sample.c
https://www.linux.com/learn/linux-training/37985-the-kernel-newbie-corner-kernel-debugging-using-proc-qsequenceq-files-part-1
*/
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h> // for sequence files
struct proc_dir_entry *pentry_sample;
char *defaultOutput = "This is testmod.";
static int my_show(struct seq_file *m, void *v)
{
seq_printf(m, "%s\n", defaultOutput);
return 0;
}
static int my_open(struct inode *inode, struct file *file)
{
return single_open(file, my_show, NULL);
}
static const struct file_operations mark_ops = {
.owner = THIS_MODULE,
.open = my_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static int __init sample_init(void)
{
printk(KERN_ALERT "sample init\n");
pentry_sample = proc_create(
"testmod-sample", 0444, NULL, &mark_ops);
if (!pentry_sample)
return -EPERM;
return 0;
}
static void __exit sample_exit(void)
{
printk(KERN_ALERT "sample exit\n");
remove_proc_entry("testmod-sample", NULL);
}
module_init(sample_init);
module_exit(sample_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Mathieu Desnoyers et al.");
MODULE_DESCRIPTION("based on Tracepoint sample");
This module can be built with the following Makefile (just have it placed in the same directory as testmod.c, and then run make in that same directory):
CONFIG_MODULE_FORCE_UNLOAD=y
# for oprofile
DEBUG_INFO=y
EXTRA_CFLAGS=-g -O0
obj-m += testmod.o
# mind the tab characters needed at start here:
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
When this module/driver is built, the output is a kernel object file, testmod.ko.
At this point, we can prepare the event tracing related to try_module_get and try_module_put; those are in /sys/kernel/debug/tracing/events/module:
$ sudo ls /sys/kernel/debug/tracing/events/module
enable filter module_free module_get module_load module_put module_request
Note that on my system, tracing is by default enabled:
$ sudo cat /sys/kernel/debug/tracing/tracing_enabled
1
... however, the module tracing (specifically) is not:
$ sudo cat /sys/kernel/debug/tracing/events/module/enable
0
Now, we should first make a filter, that will react on the module_get, module_put etc events, but only for the testmod module. To do that, we should first check the format of the event:
$ sudo cat /sys/kernel/debug/tracing/events/module/module_put/format
name: module_put
ID: 312
format:
...
field:__data_loc char[] name; offset:20; size:4; signed:1;
print fmt: "%s call_site=%pf refcnt=%d", __get_str(name), (void *)REC->ip, REC->refcnt
Here we can see that there is a field called name, which holds the driver name, which we can filter against. To create a filter, we simply echo the filter string into the corresponding file:
sudo bash -c "echo name == testmod > /sys/kernel/debug/tracing/events/module/filter"
Here, first note that since we have to call sudo, we have to wrap the whole echo redirection as an argument command of a sudo-ed bash. Second, note that since we wrote to the "parent" module/filter, not the specific events (which would be module/module_put/filter etc), this filter will be applied to all events listed as "children" of module directory.
Finally, we enable tracing for module:
sudo bash -c "echo 1 > /sys/kernel/debug/tracing/events/module/enable"
From this point on, we can read the trace log file; for me, reading the blocking,
"piped" version of the trace file worked - like this:
sudo cat /sys/kernel/debug/tracing/trace_pipe | tee tracelog.txt
At this point, we will not see anything in the log - so it is time to load (and utilize, and remove) the driver (in a different terminal from where trace_pipe is being read):
$ sudo insmod ./testmod.ko
$ cat /proc/testmod-sample
This is testmod.
$ sudo rmmod testmod
If we go back to the terminal where trace_pipe is being read, we should see something like:
# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
insmod-21137 [001] 28038.101509: module_load: testmod
insmod-21137 [001] 28038.103904: module_put: testmod call_site=sys_init_module refcnt=2
rmmod-21354 [000] 28080.244448: module_free: testmod
That is pretty much all we will obtain for our testmod driver - the refcount changes only when the driver is loaded (insmod) or unloaded (rmmod), not when we do a read through cat. So we can simply interrupt the read from trace_pipe with CTRL+C in that terminal; and to stop the tracing altogether:
sudo bash -c "echo 0 > /sys/kernel/debug/tracing/tracing_enabled"
Here, note that most examples refer to reading the file /sys/kernel/debug/tracing/trace instead of trace_pipe as here. However, one problem is that this file is not meant to be "piped" (so you shouldn't run a tail -f on this trace file); but instead you should re-read the trace after each operation. After the first insmod, we would obtain the same output from cat-ing both trace and trace_pipe; however, after the rmmod, reading the trace file would give:
<...>-21137 [001] 28038.101509: module_load: testmod
<...>-21137 [001] 28038.103904: module_put: testmod call_site=sys_init_module refcnt=2
rmmod-21354 [000] 28080.244448: module_free: testmod
... that is: at this point, the insmod had already been exited for long, and so it doesn't exist anymore in the process list - and therefore cannot be found via the recorded process ID (PID) at the time - thus we get a blank <...> as process name. Therefore, it is better to log (via tee) a running output from trace_pipe in this case. Also, note that in order to clear/reset/erase the trace file, one simply writes a 0 to it:
sudo bash -c "echo 0 > /sys/kernel/debug/tracing/trace"
If this seems counterintuitive, note that trace is a special file, and will always report a file size of zero anyways:
$ sudo ls -la /sys/kernel/debug/tracing/trace
-rw-r--r-- 1 root root 0 2013-03-19 06:39 /sys/kernel/debug/tracing/trace
... even if it is "full".
Finally, note that if we didn't implement a filter, we would have obtained a log of all module calls on the running system - which would log any call (also background) to grep and such, as those use the binfmt_misc module:
...
tr-6232 [001] 25149.815373: module_put: binfmt_misc call_site=search_binary_handler refcnt=133194
..
grep-6231 [001] 25149.816923: module_put: binfmt_misc call_site=search_binary_handler refcnt=133196
..
cut-6233 [000] 25149.817842: module_put: binfmt_misc call_site=search_binary_handler refcnt=129669
..
sudo-6234 [001] 25150.289519: module_put: binfmt_misc call_site=search_binary_handler refcnt=133198
..
tail-6235 [000] 25150.316002: module_put: binfmt_misc call_site=search_binary_handler refcnt=129671
... which adds quite a bit of overhead (in both log data ammount, and processing time required to generate it).
While looking this up, I stumbled upon Debugging Linux Kernel by Ftrace PDF, which refers to a tool trace-cmd, which pretty much does the similar as above - but through an easier command line interface. There is also a "front-end reader" GUI for trace-cmd called KernelShark; both of these are also in Debian/Ubuntu repositories via sudo apt-get install trace-cmd kernelshark. These tools could be an alternative to the procedure described above.
Finally, I'd just note that, while the above testmod example doesn't really show use in context of multiple claims, I have used the same tracing procedure to discover that an USB module I'm coding, was repeatedly claimed by pulseaudio as soon as the USB device was plugged in - so the procedure seems to work for such use cases.
| https://stackoverflow.com//questions/448999/is-there-a-way-to-figure-out-what-is-using-a-linux-kernel-module |
linux - Command to change the default home directory of a user | This question does not appear to be about programming within the scope defined in the help center. |
Ibrahim's comment on the other answer is the correct way to alter an existing user's home directory.
Change the user's home directory:
usermod -d /newhome/username username
usermod is the command to edit an existing user.
-d (abbreviation for --home) will change the user's home directory.
Change the user's home directory + Move the contents of the user's current directory:
usermod -m -d /newhome/username username
-m (abbreviation for --move-home) will move the content from the user's current directory to the new directory.
| https://stackoverflow.com//questions/20797819/command-to-change-the-default-home-directory-of-a-user |
excel - Convert xlsx to csv in Linux with command line | I'm looking for a way to convert xlsx files to csv files on Linux. |
The Gnumeric spreadsheet application comes with a command line utility called ssconvert that can convert between a variety of spreadsheet formats:
$ ssconvert Book1.xlsx newfile.csv
Using exporter Gnumeric_stf:stf_csv
$ cat newfile.csv
Foo,Bar,Baz
1,2,3
123.6,7.89,
2012/05/14,,
The,last,Line
To install on Ubuntu:
apt-get install gnumeric
To install on Mac:
brew install gnumeric
| https://stackoverflow.com//questions/10557360/convert-xlsx-to-csv-in-linux-with-command-line |
python - What is different between makedirs and mkdir of os? | I am confused to use about these two osmethods to create the new directory. |
makedirs() creates all the intermediate directories if they don't exist (just like mkdir -p in bash).
mkdir() can create a single sub-directory, and will throw an exception if intermediate directories that don't exist are specified.
Either can be used to create a single 'leaf' directory (dirA):
os.mkdir('dirA')
os.makedirs('dirA')
But makedirs must be used to create 'branches':
os.makedirs('dirA/dirB') will work [the entire structure is created]
mkdir can work here if dirA already exists, but if it doesn't an error will be thrown.
Note that unlike mkdir -p in bash, either will fail if the leaf already exists.
| https://stackoverflow.com//questions/13819496/what-is-different-between-makedirs-and-mkdir-of-os |
linux - select vs poll vs epoll | I am designing a new server which needs to support thousands of UDP connections (somewhere around 100,000 sessions). Any input or suggestions on which one to use? |
The answer is epoll if you're using Linux, kqueue if you're using FreeBSD or Mac OS X, and i/o completion ports if you're on Windows.
Some additional things you'll (almost certainly) want to research are:
Load balancing techniques
Multi-threaded networking
Database architecture
Perfect hash tables
Additionally, it is important to note that UDP does not have "connections" as opposed to TCP. It would also be in your best interest to start small and scale larger since debugging network-based solutions can be challenging.
| https://stackoverflow.com//questions/4039832/select-vs-poll-vs-epoll |
linux - How to check existence of a folder with python and then remove it? | I want to remove dataset folder from dataset3 folder. But the following code is not removing dataset.
First I want to check if dataset already exist in dataset then remove dataset.
Can some one please point out my mistake in following code? |
Python's os.rmdir() only works on empty the directories, however shutil.rmtree() doesn't care (even if there are subdirectories) which makes it very similar to the Linux rm -rf command.
import os
import shutil
dirpath = os.path.join('dataset3', 'dataset')
if os.path.exists(dirpath) and os.path.isdir(dirpath):
shutil.rmtree(dirpath)
Modern approach
In Python 3.4+ you can do same thing using the pathlib module to make the code more object-oriented and readable:
from pathlib import Path
import shutil
dirpath = Path('dataset3') / 'dataset'
if dirpath.exists() and dirpath.is_dir():
shutil.rmtree(dirpath)
| https://stackoverflow.com//questions/43765117/how-to-check-existence-of-a-folder-with-python-and-then-remove-it |
ruby on rails - cache resources exhausted Imagemagick | I'm using Imagemagick on a rails app with Minimagick and I generate some pictogram with it. |
Find the policy.xml with find / -name "policy.xml"
something like /etc/ImageMagick-6/policy.xml
and change
<policy domain="resource" name="disk" value="1GiB"/>
to
<policy domain="resource" name="disk" value="8GiB"/>
refer to convert fails due to resource limits
Memory issues
| https://stackoverflow.com//questions/31407010/cache-resources-exhausted-imagemagick |
gzip - Extract and delete all .gz in a directory- Linux | I have a directory. It has about 500K .gz files. |
This should do it:
gunzip *.gz
| https://stackoverflow.com//questions/16038087/extract-and-delete-all-gz-in-a-directory-linux |
environment variables - How does /usr/bin/env work in a Linux shebang line? | I know shebang line like this: |
env is the name of a Unix program. If you read the manual (man env) you can see that one way to use it is env COMMAND, where in your case, COMMAND is python3.
According to the manual, this will
Set each NAME to VALUE in the environment and run COMMAND.
Running env alone will show you what NAMEs and VALUEs are set:
$ env
TERM=xterm-256color
SHELL=/bin/bash
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin
…
Therefore, /usr/bin/env python3 is an instruction to set the PATH (as well as all the other NAME+VALUE pairs), and then run python3, using the first directory in the PATH that contains the python3 executable.
| https://stackoverflow.com//questions/43793040/how-does-usr-bin-env-work-in-a-linux-shebang-line |
linux - Docker error response from daemon: "Conflict ... already in use by container" | I've been using Docker on my PC to run Quantum GIS with the following instructions I've found here: docker-qgis-desktop - A simple docker container that runs QGIS desktop |
It looks like a container with the name qgis-desktop-2-4 already exists in the system. You can check the output of the below command to confirm if it indeed exists:
$ docker ps -a
The last column in the above command's output is for names.
If the container exists, remove it using:
$ docker rm qgis-desktop-2-4
Or forcefully using,
$ docker rm -f qgis-desktop-2-4
And then try creating a new container.
| https://stackoverflow.com//questions/31676155/docker-error-response-from-daemon-conflict-already-in-use-by-container |
linux - How to list files in a directory in a C program? | I'm trying to write an ftp server on Linux. In this matter how can I list files in the directory on terminal by a C program? Maybe I can use exec function to run find command but I want file name as a string to send client program. How can I do this? |
An example, available for POSIX compliant systems :
/*
* This program displays the names of all files in the current directory.
*/
#include <dirent.h>
#include <stdio.h>
int main(void) {
DIR *d;
struct dirent *dir;
d = opendir(".");
if (d) {
while ((dir = readdir(d)) != NULL) {
printf("%s\n", dir->d_name);
}
closedir(d);
}
return(0);
}
Beware that such an operation is platform dependent in C.
Source : http://faq.cprogramming.com/cgi-bin/smartfaq.cgi?answer=1046380353&id=1044780608
| https://stackoverflow.com//questions/4204666/how-to-list-files-in-a-directory-in-a-c-program |
linux - How to force 'cp' to overwrite directory instead of creating another one inside? | I'm trying to write a Bash script that will overwrite an existing directory. I have a directory foo/ and I am trying to overwrite bar/ with it. But when I do this: |
You can do this using -T option in cp.
See Man page for cp.
-T, --no-target-directory
treat DEST as a normal file
So as per your example, following is the file structure.
$ tree test
test
|-- bar
| |-- a
| `-- b
`-- foo
|-- a
`-- b
2 directories, 4 files
You can see the clear difference when you use -v for Verbose.
When you use just -R option.
$ cp -Rv foo/ bar/
`foo/' -> `bar/foo'
`foo/b' -> `bar/foo/b'
`foo/a' -> `bar/foo/a'
$ tree
|-- bar
| |-- a
| |-- b
| `-- foo
| |-- a
| `-- b
`-- foo
|-- a
`-- b
3 directories, 6 files
When you use the option -T it overwrites the contents, treating the destination like a normal file and not directory.
$ cp -TRv foo/ bar/
`foo/b' -> `bar/b'
`foo/a' -> `bar/a'
$ tree
|-- bar
| |-- a
| `-- b
`-- foo
|-- a
`-- b
2 directories, 4 files
This should solve your problem.
| https://stackoverflow.com//questions/23698183/how-to-force-cp-to-overwrite-directory-instead-of-creating-another-one-inside |
centos - How do I download a file from the internet to my linux server with Bash | Want to improve this question? Update the question so it's on-topic for Stack Overflow. |
Using wget
wget -O /tmp/myfile 'http://www.google.com/logo.jpg'
or curl:
curl -o /tmp/myfile 'http://www.google.com/logo.jpg'
| https://stackoverflow.com//questions/14300794/how-do-i-download-a-file-from-the-internet-to-my-linux-server-with-bash |
linux - How to print the ld(linker) search path | What is the way to print the search paths that in looked by ld in the order it searches. |
You can do this by executing the following command:
ld --verbose | grep SEARCH_DIR | tr -s ' ;' \\012
gcc passes a few extra -L paths to the linker, which you can list with the following command:
gcc -print-search-dirs | sed '/^lib/b 1;d;:1;s,/[^/.][^/]*/\.\./,/,;t 1;s,:[^=]*=,:;,;s,;,; ,g' | tr \; \\012
The answers suggesting to use ld.so.conf and ldconfig are not correct because they refer to the paths searched by the runtime dynamic linker (i.e. whenever a program is executed), which is not the same as the path searched by ld (i.e. whenever a program is linked).
| https://stackoverflow.com//questions/9922949/how-to-print-the-ldlinker-search-path |
Process list on Linux via Python | How can I get running process list using Python on Linux? |
IMO looking at the /proc filesystem is less nasty than hacking the text output of ps.
import os
pids = [pid for pid in os.listdir('/proc') if pid.isdigit()]
for pid in pids:
try:
print open(os.path.join('/proc', pid, 'cmdline'), 'rb').read().split('\0')
except IOError: # proc has already terminated
continue
| https://stackoverflow.com//questions/2703640/process-list-on-linux-via-python |
linux - How do I edit /etc/sudoers from a script? | I need to edit /etc/sudoers from a script to add/remove stuff from white lists. |
Old thread, but what about:
echo 'foobar ALL=(ALL:ALL) ALL' | sudo EDITOR='tee -a' visudo
| https://stackoverflow.com//questions/323957/how-do-i-edit-etc-sudoers-from-a-script |
Shebang Notation: Python Scripts on Windows and Linux? | I have some small utility scripts written in Python that I want to be usable on both Windows and Linux. I want to avoid having to explicitly invoke the Python interpreter. Is there an easy way to point shebang notation to the correct locations on both Windows and Linux? If not, is there another way to allow implicit invocation of the Python interpreter on both Windows and Linux without having to modify the script when transferring between operating systems? |
Read up on the Python Launcher for Windows in the docs, which was initially described in PEP 397. It lets
you define custom shebang configurations in "py.ini" (e.g. to use pypy),
and out of the box you can use virtual shebangs such as #!/usr/bin/env python3, or shebangs with real paths such as #!"C:\Python33\python.exe". (Quoting is required for paths containing spaces.) You can also add command-line options to a shebang. For example, the following shebang adds the option to enter interactive mode after the script terminates: #!/usr/bin/python3 -i.
The installer associates .py (console) and .pyw (GUI) script file types with the respectively named launchers, py.exe and pyw.exe, in order to enable shebang support for scripts in Windows. For an all-users installation, the launchers are installed to the Windows folder (i.e. %SystemRoot%). For a per-user installation, you may need to manually add the installation directory to PATH in order to use py.exe in the shell (*). Then from the command line you can run Python via py -2, py -3, py -2.6, py -3.3-32 (32-bit), and so on. The launcher is handy when combined with -m to run a module as a script using a particular version of the interpreter, e.g. py -3 -m pip install.
(*) The new installer in 3.5+ defaults to "%LocalAppData%\Programs\Python\Launcher" for a per-user installation of the launcher, instead of installing it beside "python.exe", and it automatically adds this directory to PATH.
| https://stackoverflow.com//questions/7574453/shebang-notation-python-scripts-on-windows-and-linux |
linux - fork: retry: Resource temporarily unavailable | Want to improve this question? Update the question so it's on-topic for Stack Overflow. |
This is commonly caused by running out of file descriptors.
There is the systems total file descriptor limit, what do you get from the command:
sysctl fs.file-nr
This returns counts of file descriptors:
<in_use> <unused_but_allocated> <maximum>
To find out what a users file descriptor limit is run the commands:
sudo su - <username>
ulimit -Hn
To find out how many file descriptors are in use by a user run the command:
sudo lsof -u <username> 2>/dev/null | wc -l
So now if you are having a system file descriptor limit issue you will need to edit your /etc/sysctl.conf file and add, or modify it it already exists, a line with fs.file-max and set it to a value large enough to deal with the number of file descriptors you need and reboot.
fs.file-max = 204708
| https://stackoverflow.com//questions/12079087/fork-retry-resource-temporarily-unavailable |
linux - grep exclude multiple strings | I am trying to see a log file using tail -f and want to exclude all lines containing the following strings: |
Filtering out multiple lines with grep:
Put these lines in filename.txt to test:
abc
def
ghi
jkl
grep command using -E flag with a pipe between tokens in a string:
grep -Ev 'def|jkl' filename.txt
prints:
abc
ghi
egrep using -v flag with pipe between tokens surrounded by parens:
egrep -v '(def|jkl)' filename.txt
prints:
abc
ghi
Or if stacking -e flags through grep parameters is okay (credit -> @Frizlab):
grep -Fv -e def -e jkl filename.txt
prints:
abc
ghi
| https://stackoverflow.com//questions/16212656/grep-exclude-multiple-strings |
logging - View a log file in Linux dynamically | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
tail -f yourlog.csv
Newly appended lines will continuously show.
| https://stackoverflow.com//questions/2099149/view-a-log-file-in-linux-dynamically |
linux - What is better, curl or wget? | Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. |
If you are programming, you should use curl. It has a nice api and is available for most languages. Shelling out to the os to run wget is a kludge and shouldn't be done if you have an API interface!
| https://stackoverflow.com//questions/636339/what-is-better-curl-or-wget |
c - What is the role of libc(glibc) in our linux app? | When we debug a program using gdb, we usually see functions with strange names defined in libc(glibc?). My questions are: |
libc implements both standard C functions like strcpy() and POSIX functions (which may be system calls) like getpid(). Note that not all standard C functions are in libc - most math functions are in libm.
You cannot directly make system calls in the same way that you call normal functions because calls to the kernel aren't normal function calls, so they can't be resolved by the linker. Instead, architecture-specific assembly language thunks are used to call into the kernel - you can of course write these directly in your own program too, but you don't need to because libc provides them for you.
Note that in Linux it is the combination of the kernel and libc that provides the POSIX API. libc adds a decent amount of value - not every POSIX function is necessarily a system call, and for the ones that are, the kernel behaviour isn't always POSIX conforming.
libc is a single library file (both .so and .a versions are available) and in most cases resides in /usr/lib. However, the glibc (GNU libc) project provides more than just libc - it also provides the libm mentioned earlier, and other core libraries like libpthread. So libc is just one of the libraries provided by glibc - and there are other alternate implementations of libc other than glibc.
| https://stackoverflow.com//questions/11372872/what-is-the-role-of-libcglibc-in-our-linux-app |
linux - How many socket connections possible? | Has anyone an idea how many tcp-socket connections are possible on a modern standard Linux server? |
I achieved 1600k concurrent idle socket connections, and at the same time 57k req/s on a Linux desktop (16G RAM, I7 2600 CPU). It's a single thread http server written in C with epoll. Source code is on github, a blog here.
Edit:
I did 600k concurrent HTTP connections (client & server) on both the same computer, with JAVA/Clojure . detail info post, HN discussion: http://news.ycombinator.com/item?id=5127251
The cost of a connection(with epoll):
application need some RAM per connection
TCP buffer 2 * 4k ~ 10k, or more
epoll need some memory for a file descriptor, from epoll(7)
Each registered file descriptor costs roughly 90
bytes on a 32-bit kernel, and roughly 160 bytes on a 64-bit kernel.
| https://stackoverflow.com//questions/651665/how-many-socket-connections-possible |
Best way to find os name and version in Unix/Linux platform | I need to find the OS name and version on Unix/Linux platform. For this I tried following: |
This work fine for all Linux environment.
#!/bin/sh
cat /etc/*-release
In Ubuntu:
$ cat /etc/*-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.04
DISTRIB_CODENAME=lucid
DISTRIB_DESCRIPTION="Ubuntu 10.04.4 LTS"
or 12.04:
$ cat /etc/*-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu 12.04.4 LTS"
NAME="Ubuntu"
VERSION="12.04.4 LTS, Precise Pangolin"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu precise (12.04.4 LTS)"
VERSION_ID="12.04"
In RHEL:
$ cat /etc/*-release
Red Hat Enterprise Linux Server release 6.5 (Santiago)
Red Hat Enterprise Linux Server release 6.5 (Santiago)
Or Use this Script:
#!/bin/sh
# Detects which OS and if it is Linux then it will detect which Linux
# Distribution.
OS=`uname -s`
REV=`uname -r`
MACH=`uname -m`
GetVersionFromFile()
{
VERSION=`cat $1 | tr "\n" ' ' | sed s/.*VERSION.*=\ // `
}
if [ "${OS}" = "SunOS" ] ; then
OS=Solaris
ARCH=`uname -p`
OSSTR="${OS} ${REV}(${ARCH} `uname -v`)"
elif [ "${OS}" = "AIX" ] ; then
OSSTR="${OS} `oslevel` (`oslevel -r`)"
elif [ "${OS}" = "Linux" ] ; then
KERNEL=`uname -r`
if [ -f /etc/redhat-release ] ; then
DIST='RedHat'
PSUEDONAME=`cat /etc/redhat-release | sed s/.*\(// | sed s/\)//`
REV=`cat /etc/redhat-release | sed s/.*release\ // | sed s/\ .*//`
elif [ -f /etc/SuSE-release ] ; then
DIST=`cat /etc/SuSE-release | tr "\n" ' '| sed s/VERSION.*//`
REV=`cat /etc/SuSE-release | tr "\n" ' ' | sed s/.*=\ //`
elif [ -f /etc/mandrake-release ] ; then
DIST='Mandrake'
PSUEDONAME=`cat /etc/mandrake-release | sed s/.*\(// | sed s/\)//`
REV=`cat /etc/mandrake-release | sed s/.*release\ // | sed s/\ .*//`
elif [ -f /etc/debian_version ] ; then
DIST="Debian `cat /etc/debian_version`"
REV=""
fi
if [ -f /etc/UnitedLinux-release ] ; then
DIST="${DIST}[`cat /etc/UnitedLinux-release | tr "\n" ' ' | sed s/VERSION.*//`]"
fi
OSSTR="${OS} ${DIST} ${REV}(${PSUEDONAME} ${KERNEL} ${MACH})"
fi
echo ${OSSTR}
| https://stackoverflow.com//questions/26988262/best-way-to-find-os-name-and-version-in-unix-linux-platform |
java - Linux command for extracting war file? | How can I extract a .war file with Linux command prompt? |
Using unzip
unzip -c whatever.war META-INF/MANIFEST.MF
It will print the output in terminal.
And for extracting all the files,
unzip whatever.war
Using jar
jar xvf test.war
Note! The jar command will extract war contents to current directory. Not to a subdirectory (like Tomcat does).
| https://stackoverflow.com//questions/3833578/linux-command-for-extracting-war-file |
How to list empty folders in linux | In Linux how do I check all folders in a directory and output the name of all directories that are empty to a list. |
Try the following:
find . -type d -empty
| https://stackoverflow.com//questions/9417967/how-to-list-empty-folders-in-linux |
Linux error while loading shared libraries: cannot open shared object file: No such file or directory | Program is part of the Xenomai test suite, cross-compiled from Linux PC into Linux+Xenomai ARM toolchain. |
Your library is a dynamic library.
You need to tell the operating system where it can locate it at runtime.
To do so,
we will need to do those easy steps:
Find where the library is placed if you don't know it.
sudo find / -name the_name_of_the_file.so
Check for the existence of the dynamic library path environment variable(LD_LIBRARY_PATH)
echo $LD_LIBRARY_PATH
If there is nothing to be displayed, add a default path value (or not if you wish to)
LD_LIBRARY_PATH=/usr/local/lib
We add the desired path, export it and try the application.
Note that the path should be the directory where the path.so.something is. So if path.so.something is in /my_library/path.so.something, it should be:
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/my_library/
export LD_LIBRARY_PATH
./my_app
Reference to source
| https://stackoverflow.com//questions/480764/linux-error-while-loading-shared-libraries-cannot-open-shared-object-file-no-s |
Shebang Notation: Python Scripts on Windows and Linux? | I have some small utility scripts written in Python that I want to be usable on both Windows and Linux. I want to avoid having to explicitly invoke the Python interpreter. Is there an easy way to point shebang notation to the correct locations on both Windows and Linux? If not, is there another way to allow implicit invocation of the Python interpreter on both Windows and Linux without having to modify the script when transferring between operating systems? |
Read up on the Python Launcher for Windows in the docs, which was initially described in PEP 397. It lets
you define custom shebang configurations in "py.ini" (e.g. to use pypy),
and out of the box you can use virtual shebangs such as #!/usr/bin/env python3, or shebangs with real paths such as #!"C:\Python33\python.exe". (Quoting is required for paths containing spaces.) You can also add command-line options to a shebang. For example, the following shebang adds the option to enter interactive mode after the script terminates: #!/usr/bin/python3 -i.
The installer associates .py (console) and .pyw (GUI) script file types with the respectively named launchers, py.exe and pyw.exe, in order to enable shebang support for scripts in Windows. For an all-users installation, the launchers are installed to the Windows folder (i.e. %SystemRoot%). For a per-user installation, you may need to manually add the installation directory to PATH in order to use py.exe in the shell (*). Then from the command line you can run Python via py -2, py -3, py -2.6, py -3.3-32 (32-bit), and so on. The launcher is handy when combined with -m to run a module as a script using a particular version of the interpreter, e.g. py -3 -m pip install.
(*) The new installer in 3.5+ defaults to "%LocalAppData%\Programs\Python\Launcher" for a per-user installation of the launcher, instead of installing it beside "python.exe", and it automatically adds this directory to PATH.
| https://stackoverflow.com//questions/7574453/shebang-notation-python-scripts-on-windows-and-linux |
linux - How many socket connections possible? | Has anyone an idea how many tcp-socket connections are possible on a modern standard Linux server? |
I achieved 1600k concurrent idle socket connections, and at the same time 57k req/s on a Linux desktop (16G RAM, I7 2600 CPU). It's a single thread http server written in C with epoll. Source code is on github, a blog here.
Edit:
I did 600k concurrent HTTP connections (client & server) on both the same computer, with JAVA/Clojure . detail info post, HN discussion: http://news.ycombinator.com/item?id=5127251
The cost of a connection(with epoll):
application need some RAM per connection
TCP buffer 2 * 4k ~ 10k, or more
epoll need some memory for a file descriptor, from epoll(7)
Each registered file descriptor costs roughly 90
bytes on a 32-bit kernel, and roughly 160 bytes on a 64-bit kernel.
| https://stackoverflow.com//questions/651665/how-many-socket-connections-possible |
linux - nginx not listening to port 80 | I've just installed a Ubuntu 12.04 server and nginx 1.2.7, removed default from sites-enabled and added my own file into sites-available and symlink at sites-enabled. Then restarted nginx. |
I had this same problem, the solution was that I had not symlinked my siteconf file correctly. Try running vim /etc/nginx/sites-enabled/mysite.com—can you get to it? I was getting "Permission Denied."
If not run:
rm /etc/nginx/sites-enabled/mysite.com
ln -s /etc/nginx/sites-available/mysite.com /etc/nginx/sites-enabled/mysite.com
| https://stackoverflow.com//questions/16021481/nginx-not-listening-to-port-80 |
Locking Executing Files: Windows does, Linux doesn't. Why? | I noticed when a file is executed on Windows (.exe or .dll), it is locked and cannot be deleted, moved or modified. |
Linux has a reference-count mechanism, so you can delete the file while it is executing, and it will continue to exist as long as some process (Which previously opened it) has an open handle for it. The directory entry for the file is removed when you delete it, so it cannot be opened any more, but processes already using this file can still use it. Once all processes using this file terminate, the file is deleted automatically.
Windows does not have this capability, so it is forced to lock the file until all processes executing from it have finished.
I believe that the Linux behavior is preferable. There are probably some deep architectural reasons, but the prime (and simple) reason I find most compelling is that in Windows, you sometimes cannot delete a file, you have no idea why, and all you know is that some process is keeping it in use. In Linux it never happens.
| https://stackoverflow.com//questions/196897/locking-executing-files-windows-does-linux-doesnt-why |
How can I identify the request queue for a linux block device | I am working on this driver that connects the hard disk over the network. There is a bug that if I enable two or more hard disks on the computer, only the first one gets the partitions looked over and identified. The result is, if I have 1 partition on hda and 1 partitions on hdb, as soon as I connect hda there is a partition that can be mounted. So hda1 gets a blkid xyz123 as soon as it mounts. But when I go ahead and mount hdb1 it also comes up with the same blkid and in fact, the driver is reading it from hda, not hdb. |
Queue = blk_init_queue(sbd_request, &Device.lock);
| https://stackoverflow.com//questions/6785651/how-can-i-identify-the-request-queue-for-a-linux-block-device |
c - What does opening a file actually do? | In all programming languages (that I use at least), you must open a file before you can read or write to it. |
In almost every high-level language, the function that opens a file is a wrapper around the corresponding kernel system call. It may do other fancy stuff as well, but in contemporary operating systems, opening a file must always go through the kernel.
This is why the arguments of the fopen library function, or Python's open closely resemble the arguments of the open(2) system call.
In addition to opening the file, these functions usually set up a buffer that will be consequently used with the read/write operations. The purpose of this buffer is to ensure that whenever you want to read N bytes, the corresponding library call will return N bytes, regardless of whether the calls to the underlying system calls return less.
I am not actually interested in implementing my own function; just in understanding what the hell is going on...'beyond the language' if you like.
In Unix-like operating systems, a successful call to open returns a "file descriptor" which is merely an integer in the context of the user process. This descriptor is consequently passed to any call that interacts with the opened file, and after calling close on it, the descriptor becomes invalid.
It is important to note that the call to open acts like a validation point at which various checks are made. If not all of the conditions are met, the call fails by returning -1 instead of the descriptor, and the kind of error is indicated in errno. The essential checks are:
Whether the file exists;
Whether the calling process is privileged to open this file in the specified mode. This is determined by matching the file permissions, owner ID and group ID to the respective ID's of the calling process.
In the context of the kernel, there has to be some kind of mapping between the process' file descriptors and the physically opened files. The internal data structure that is mapped to the descriptor may contain yet another buffer that deals with block-based devices, or an internal pointer that points to the current read/write position.
| https://stackoverflow.com//questions/33495283/what-does-opening-a-file-actually-do |
linux - IPC performance: Named Pipe vs Socket | Everyone seems to say named pipes are faster than sockets IPC. How much faster are they? I would prefer to use sockets because they can do two-way communication and are very flexible but will choose speed over flexibility if it is by considerable amount. |
Best results you'll get with Shared Memory solution.
Named pipes are only 16% better than TCP sockets.
Results are get with IPC benchmarking:
System: Linux (Linux ubuntu 4.4.0 x86_64 i7-6700K 4.00GHz)
Message: 128 bytes
Messages count: 1000000
Pipe benchmark:
Message size: 128
Message count: 1000000
Total duration: 27367.454 ms
Average duration: 27.319 us
Minimum duration: 5.888 us
Maximum duration: 15763.712 us
Standard deviation: 26.664 us
Message rate: 36539 msg/s
FIFOs (named pipes) benchmark:
Message size: 128
Message count: 1000000
Total duration: 38100.093 ms
Average duration: 38.025 us
Minimum duration: 6.656 us
Maximum duration: 27415.040 us
Standard deviation: 91.614 us
Message rate: 26246 msg/s
Message Queue benchmark:
Message size: 128
Message count: 1000000
Total duration: 14723.159 ms
Average duration: 14.675 us
Minimum duration: 3.840 us
Maximum duration: 17437.184 us
Standard deviation: 53.615 us
Message rate: 67920 msg/s
Shared Memory benchmark:
Message size: 128
Message count: 1000000
Total duration: 261.650 ms
Average duration: 0.238 us
Minimum duration: 0.000 us
Maximum duration: 10092.032 us
Standard deviation: 22.095 us
Message rate: 3821893 msg/s
TCP sockets benchmark:
Message size: 128
Message count: 1000000
Total duration: 44477.257 ms
Average duration: 44.391 us
Minimum duration: 11.520 us
Maximum duration: 15863.296 us
Standard deviation: 44.905 us
Message rate: 22483 msg/s
Unix domain sockets benchmark:
Message size: 128
Message count: 1000000
Total duration: 24579.846 ms
Average duration: 24.531 us
Minimum duration: 2.560 us
Maximum duration: 15932.928 us
Standard deviation: 37.854 us
Message rate: 40683 msg/s
ZeroMQ benchmark:
Message size: 128
Message count: 1000000
Total duration: 64872.327 ms
Average duration: 64.808 us
Minimum duration: 23.552 us
Maximum duration: 16443.392 us
Standard deviation: 133.483 us
Message rate: 15414 msg/s
| https://stackoverflow.com//questions/1235958/ipc-performance-named-pipe-vs-socket |
linux - Why doesn't a shell get variables exported by a script run in a subshell? | I have two scripts 1.sh and 2.sh. |
If you are executing your files like sh 1.sh or ./1.sh Then you are executing it in a sub-shell.
If you want the changes to be made in your current shell, you could do:
. 1.sh
# OR
source 1.sh
Please consider going through the reference-documentation.
"When a script is run using source [or .] it runs within the existing shell, any variables created or modified by the script will remain available after the script completes. In contrast if the script is run just as filename, then a separate subshell (with a completely separate set of variables) would be spawned to run the script."
| https://stackoverflow.com//questions/10781824/why-doesnt-a-shell-get-variables-exported-by-a-script-run-in-a-subshell |
java - Moving from JDK 1.7 to JDK 1.8 on Ubuntu | I am on UBUNTU. JDK version currently installed is: |
This is what I do on debian - I suspect it should work on ubuntu (amend the version as required + adapt the folder where you want to copy the JDK files as you wish, I'm using /opt/jdk):
wget --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u71-b15/jdk-8u71-linux-x64.tar.gz
sudo mkdir /opt/jdk
sudo tar -zxf jdk-8u71-linux-x64.tar.gz -C /opt/jdk/
rm jdk-8u71-linux-x64.tar.gz
Then update-alternatives:
sudo update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_71/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_71/bin/javac 1
Select the number corresponding to the /opt/jdk/jdk1.8.0_71/bin/java when running the following commands:
sudo update-alternatives --config java
sudo update-alternatives --config javac
Finally, verify that the correct version is selected:
java -version
javac -version
| https://stackoverflow.com//questions/30177455/moving-from-jdk-1-7-to-jdk-1-8-on-ubuntu |
linux - Run an Ansible task only when the variable contains a specific string | I have multiple tasks depend from the value of variable1. I want to check if the value is in {{ variable1 }} but I get an error: |
If variable1 is a string, and you are searching for a substring in it, this should work:
when: '"value" in variable1'
if variable1 is an array or dict instead, in will search for the exact string as one of its items.
| https://stackoverflow.com//questions/36496911/run-an-ansible-task-only-when-the-variable-contains-a-specific-string |
linux - How do I measure separate CPU core usage for a process? | Is there any way to measure a specific process CPU usage by cores? |
You can still do this in top. While top is running, press '1' on your keyboard, it will then show CPU usage per core.
Limit the processes shown by having that specific process run under a specific user account and use Type 'u' to limit to that user
| https://stackoverflow.com//questions/3342889/how-do-i-measure-separate-cpu-core-usage-for-a-process |
linux - Avoid gnome-terminal close after script execution? | I created a bash script that opens several gnome-terminals, connect to classroom computers via ssh and run a script. |
As I understand you want gnome-terminal to open, have it execute some commands, and then drop to the prompt so you can enter some more commands. Gnome-terminal is not designed for this use case, but there are workarounds:
Let gnome-terminal run bash and tell bash to run your commands and then start a new bash
$ gnome-terminal -- bash -c "echo foo; echo bar; exec bash"
or if the commands are in a script
$ gnome-terminal -- bash -c "./scripttorun; exec bash"
The first bash will terminate once all the commands are done. But the last command is a new bash which will then just keep running. And since something is still running gnome-terminal will not close.
Let gnome-terminal run bash with a prepared rcfile which runs your commands
Prepare somercfile:
source ~/.bashrc
echo foo
echo bar
Then run:
$ gnome-terminal -- bash --rcfile somercfile
bash will stay open after running somercfile.
i must admit i do not understand completely why --rcfile has this behaviour but it does.
Let gnome-terminal run a script which runs your commands and then drops to bash
Prepare scripttobash:
#!/bin/sh
echo foo
echo bar
exec bash
Set this file as executable.
Then run:
$ gnome-terminal -- ./scripttobash
for completeness
if you just want to be able read the output of the command and need no interactivity
go to preferences (hamburger button -> preferences)
go to profiles (standard or create a new one)
go to command tab
when command exits -> hold the terminal open
i recommend to create a new profile for just for this use case.
use the profile like this:
gnome-terminal --profile=holdopen -- ./scripttorun
Every method has it's quirks. You must choose, but choose wisely.
I like the first solution. it does not need extra files or profiles. and the command says what it does: run commands then run bash again.
All that said, since you used ssh in your example, you might want to take a look at pssh (parallel ssh). here an article: https://www.cyberciti.biz/cloud-computing/how-to-use-pssh-parallel-ssh-program-on-linux-unix/
| https://stackoverflow.com//questions/3512055/avoid-gnome-terminal-close-after-script-execution |
linux - Read and write to binary files in C? | Does anyone have an example of code that can write to a binary file. And also code that can read a binary file and output to screen. Looking at examples I can write to a file ok But when I try to read from a file it is not outputting correctly. |
Reading and writing binary files is pretty much the same as any other file, the only difference is how you open it:
unsigned char buffer[10];
FILE *ptr;
ptr = fopen("test.bin","rb"); // r for read, b for binary
fread(buffer,sizeof(buffer),1,ptr); // read 10 bytes to our buffer
You said you can read it, but it's not outputting correctly... keep in mind that when you "output" this data, you're not reading ASCII, so it's not like printing a string to the screen:
for(int i = 0; i<10; i++)
printf("%u ", buffer[i]); // prints a series of bytes
Writing to a file is pretty much the same, with the exception that you're using fwrite() instead of fread():
FILE *write_ptr;
write_ptr = fopen("test.bin","wb"); // w for write, b for binary
fwrite(buffer,sizeof(buffer),1,write_ptr); // write 10 bytes from our buffer
Since we're talking Linux.. there's an easy way to do a sanity check. Install hexdump on your system (if it's not already on there) and dump your file:
mike@mike-VirtualBox:~/C$ hexdump test.bin
0000000 457f 464c 0102 0001 0000 0000 0000 0000
0000010 0001 003e 0001 0000 0000 0000 0000 0000
...
Now compare that to your output:
mike@mike-VirtualBox:~/C$ ./a.out
127 69 76 70 2 1 1 0 0 0
hmm, maybe change the printf to a %x to make this a little clearer:
mike@mike-VirtualBox:~/C$ ./a.out
7F 45 4C 46 2 1 1 0 0 0
Hey, look! The data matches up now*. Awesome, we must be reading the binary file correctly!
*Note the bytes are just swapped on the output but that data is correct, you can adjust for this sort of thing
| https://stackoverflow.com//questions/17598572/read-and-write-to-binary-files-in-c |
linux - tcp_tw_reuse vs tcp_tw_recycle : Which to use (or both)? | I have a website and application which use a significant number of connections. It normally has about 3,000 connections statically open, and can receive anywhere from 5,000 to 50,000 connection attempts in a few seconds time frame. |
According to Linux documentation, you should use the TCP_TW_REUSE flag to allow reusing sockets in TIME_WAIT state for new connections.
It seems to be a good option when dealing with a web server that have to handle many short TCP connections left in a TIME_WAIT state.
As described here, The TCP_TW_RECYCLE could cause some problems when using load balancers...
EDIT (to add some warnings ;) ):
as mentionned in comment by @raittes, the "problems when using load balancers" is about public-facing servers. When recycle is enabled, the server can't distinguish new incoming connections from different clients behind the same NAT device.
| https://stackoverflow.com//questions/6426253/tcp-tw-reuse-vs-tcp-tw-recycle-which-to-use-or-both |
windows - Cross-platform space remaining on volume using python | I need a way to determine the space remaining on a disk volume using python on linux, Windows and OS X. I'm currently parsing the output of the various system calls (df, dir) to accomplish this - is there a better way? |
import ctypes
import os
import platform
import sys
def get_free_space_mb(dirname):
"""Return folder/drive free space (in megabytes)."""
if platform.system() == 'Windows':
free_bytes = ctypes.c_ulonglong(0)
ctypes.windll.kernel32.GetDiskFreeSpaceExW(ctypes.c_wchar_p(dirname), None, None, ctypes.pointer(free_bytes))
return free_bytes.value / 1024 / 1024
else:
st = os.statvfs(dirname)
return st.f_bavail * st.f_frsize / 1024 / 1024
Note that you must pass a directory name for GetDiskFreeSpaceEx() to work
(statvfs() works on both files and directories). You can get a directory name
from a file with os.path.dirname().
Also see the documentation for os.statvfs() and GetDiskFreeSpaceEx.
| https://stackoverflow.com//questions/51658/cross-platform-space-remaining-on-volume-using-python |
linux - Using iconv to convert from UTF-16LE to UTF-8 | Hi I am trying to convert some log files from a Microsoft SQL server, but the files are encoded using UTf-16LE and iconv does not seem to be able to convert them. |
I forgot the -o switch!
The final command is :
iconv -f UTF-16LE -t UTF-8 <filename> -o <new-filename>
| https://stackoverflow.com//questions/17287713/using-iconv-to-convert-from-utf-16le-to-utf-8 |
mysql - Job for mysqld.service failed See "systemctl status mysqld.service" | Console says |
This amazingly worked.
/etc/init.d/mysql stop
service mysql stop
killall -KILL mysql mysqld_safe mysqld
/etc/init.d/mysql start
service mysql start
| https://stackoverflow.com//questions/42317139/job-for-mysqld-service-failed-see-systemctl-status-mysqld-service |
linux - Is it better to use git grep than plain grep if we want to search in versioned source code? | In a git repository, is there any difference/benefit using git grep over good old grep?
An example would be? |
The two are very similar. The main difference is that git grep defaults to searching in the files that are tracked by git.
Examples
If I want to find foo within my project I can use git grep or good ol' stand-alone grep:
git grep foo
grep -R foo .
The git grep version will only search in files tracked by git, whereas the grep version will search everything in the directory. So far so similar; either one could be better depending on what you want to achieve.
What if we want to limit the search to only .rb files?
git grep foo -- *.rb
grep -R --include=*.rb foo .
The plain old grep version is getting a bit more wordy, but if you're used to using grep that may not be a problem. They're still not going to search exactly the same files, but again it depends on what you want to achieve.
What about searching in the previous version of the project?
git grep foo HEAD^
git checkout HEAD^; grep -R foo .; git checkout -
This is where git grep makes a real difference: You can search in another revision of the project without checking it out first. This isn't a situation that comes up too often for me though; I usually want to search in the version of the project I have checked out.
Configuring git grep
There are some git config variables that modify the behaviour of git grep and avoid the need to pass a couple of command line arguments:
grep.lineNumber: Always show line numbers of matches (you can pass -n to both grep and git grep to get this behaviour)
grep.extendedRegexp: Always use extended regular expressions (you can pass -E to both grep and git grep to get this behaviour)
In practice
In practice I have gg aliased to git grep -En, and this almost always does what I want.
| https://stackoverflow.com//questions/17557684/is-it-better-to-use-git-grep-than-plain-grep-if-we-want-to-search-in-versioned-s |
linux - How to write stdout to file with colors? | A lot of times (not always) the stdout is displayed in colors. Normally I keep every output log in a different file too. Naturally in the file, the colors are not displayed anymore. |
Since many programs will only output color sequences if their stdout is a terminal, a general solution to this problem requires tricking them into believing that the pipe they write to is a terminal. This is possible with the script command from bsdutils:
script -q -c "vagrant up" filename.txt
This will write the output from vagrant up to filename.txt (and the terminal). If echoing is not desirable,
script -q -c "vagrant up" filename > /dev/null
will write it only to the file.
| https://stackoverflow.com//questions/27397865/how-to-write-stdout-to-file-with-colors |
linux - Get exit code of a background process | I have a command CMD called from my main bourne shell script that takes forever. |
1: In bash, $! holds the PID of the last background process that was executed. That will tell you what process to monitor, anyway.
4: wait <n> waits until the process with PID <n> is complete (it will block until the process completes, so you might not want to call this until you are sure the process is done), and then returns the exit code of the completed process.
2, 3: ps or ps | grep " $! " can tell you whether the process is still running. It is up to you how to understand the output and decide how close it is to finishing. (ps | grep isn't idiot-proof. If you have time you can come up with a more robust way to tell whether the process is still running).
Here's a skeleton script:
# simulate a long process that will have an identifiable exit code
(sleep 15 ; /bin/false) &
my_pid=$!
while ps | grep " $my_pid " # might also need | grep -v grep here
do
echo $my_pid is still in the ps output. Must still be running.
sleep 3
done
echo Oh, it looks like the process is done.
wait $my_pid
# The variable $? always holds the exit code of the last command to finish.
# Here it holds the exit code of $my_pid, since wait exits with that code.
my_status=$?
echo The exit status of the process was $my_status
| https://stackoverflow.com//questions/1570262/get-exit-code-of-a-background-process |
linux - Is Mac OS X a POSIX OS? | What is it that makes an OS a POSIX system? All versions of Linux are POSIX, right? What about Mac OS X? |
Is Mac OS X a POSIX OS?
Yes.
POSIX is a group of standards that determine a portable API for Unix-like operating systems. Mac OS X is Unix-based (and has been certified as such), and in accordance with this is POSIX compliant. POSIX guarantees that certain system calls will be available.
Essentially, Mac satisfies the API required to be POSIX compliant, which makes it a POSIX OS.
All versions of Linux are not POSIX-compliant. Kernel versions prior to 2.6 were not compliant, and today Linux isn't officially POSIX-compliant because they haven't gone out of their way to get certified (which will likely never happen). Regardless, Linux can be treated as a POSIX system for almost all intents and purposes.
| https://stackoverflow.com//questions/5785516/is-mac-os-x-a-posix-os |
linux - Avoid gnome-terminal close after script execution? | I created a bash script that opens several gnome-terminals, connect to classroom computers via ssh and run a script. |
As I understand you want gnome-terminal to open, have it execute some commands, and then drop to the prompt so you can enter some more commands. Gnome-terminal is not designed for this use case, but there are workarounds:
Let gnome-terminal run bash and tell bash to run your commands and then start a new bash
$ gnome-terminal -- bash -c "echo foo; echo bar; exec bash"
or if the commands are in a script
$ gnome-terminal -- bash -c "./scripttorun; exec bash"
The first bash will terminate once all the commands are done. But the last command is a new bash which will then just keep running. And since something is still running gnome-terminal will not close.
Let gnome-terminal run bash with a prepared rcfile which runs your commands
Prepare somercfile:
source ~/.bashrc
echo foo
echo bar
Then run:
$ gnome-terminal -- bash --rcfile somercfile
bash will stay open after running somercfile.
i must admit i do not understand completely why --rcfile has this behaviour but it does.
Let gnome-terminal run a script which runs your commands and then drops to bash
Prepare scripttobash:
#!/bin/sh
echo foo
echo bar
exec bash
Set this file as executable.
Then run:
$ gnome-terminal -- ./scripttobash
for completeness
if you just want to be able read the output of the command and need no interactivity
go to preferences (hamburger button -> preferences)
go to profiles (standard or create a new one)
go to command tab
when command exits -> hold the terminal open
i recommend to create a new profile for just for this use case.
use the profile like this:
gnome-terminal --profile=holdopen -- ./scripttorun
Every method has it's quirks. You must choose, but choose wisely.
I like the first solution. it does not need extra files or profiles. and the command says what it does: run commands then run bash again.
All that said, since you used ssh in your example, you might want to take a look at pssh (parallel ssh). here an article: https://www.cyberciti.biz/cloud-computing/how-to-use-pssh-parallel-ssh-program-on-linux-unix/
| https://stackoverflow.com//questions/3512055/avoid-gnome-terminal-close-after-script-execution |
linux - Setting up FTP on Amazon Cloud Server | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
Jaminto did a great job of answering the question, but I recently went through the process myself and wanted to expand on Jaminto's answer.
I'm assuming that you already have an EC2 instance created and have associated an Elastic IP Address to it.
Step #1: Install vsftpd
SSH to your EC2 server. Type:
> sudo yum install vsftpd
This should install vsftpd.
Step #2: Open up the FTP ports on your EC2 instance
Next, you'll need to open up the FTP ports on your EC2 server. Log in to the AWS EC2 Management Console and select Security Groups from the navigation tree on the left. Select the security group assigned to your EC2 instance. Then select the Inbound tab, then click Edit:
Add two Custom TCP Rules with port ranges 20-21 and 1024-1048. For Source, you can select 'Anywhere'. If you decide to set Source to your own IP address, be aware that your IP address might change if it is being assigned via DHCP.
Step #3: Make updates to the vsftpd.conf file
Edit your vsftpd conf file by typing:
> sudo vi /etc/vsftpd/vsftpd.conf
Disable anonymous FTP by changing this line:
anonymous_enable=YES
to
anonymous_enable=NO
Then add the following lines to the bottom of the vsftpd.conf file:
pasv_enable=YES
pasv_min_port=1024
pasv_max_port=1048
pasv_address=<Public IP of your instance>
Your vsftpd.conf file should look something like the following - except make sure to replace the pasv_address with your public facing IP address:
To save changes, press escape, then type :wq, then hit enter.
Step #4: Restart vsftpd
Restart vsftpd by typing:
> sudo /etc/init.d/vsftpd restart
You should see a message that looks like:
If this doesn't work, try:
> sudo /sbin/service vsftpd restart
Step #5: Create an FTP user
If you take a peek at /etc/vsftpd/user_list, you'll see the following:
# vsftpd userlist
# If userlist_deny=NO, only allow users in this file
# If userlist_deny=YES (default), never allow users in this file, and
# do not even prompt for a password.
# Note that the default vsftpd pam config also checks /etc/vsftpd/ftpusers
# for users that are denied.
root
bin
daemon
adm
lp
sync
shutdown
halt
mail
news
uucp
operator
games
nobody
This is basically saying, "Don't allow these users FTP access." vsftpd will allow FTP access to any user not on this list.
So, in order to create a new FTP account, you may need to create a new user on your server. (Or, if you already have a user account that's not listed in /etc/vsftpd/user_list, you can skip to the next step.)
Creating a new user on an EC2 instance is pretty simple. For example, to create the user 'bret', type:
> sudo adduser bret
> sudo passwd bret
Here's what it will look like:
Step #6: Restricting users to their home directories
At this point, your FTP users are not restricted to their home directories. That's not very secure, but we can fix it pretty easily.
Edit your vsftpd conf file again by typing:
> sudo vi /etc/vsftpd/vsftpd.conf
Un-comment out the line:
chroot_local_user=YES
It should look like this once you're done:
Restart the vsftpd server again like so:
> sudo /etc/init.d/vsftpd restart
All done!
Appendix A: Surviving a reboot
vsftpd doesn't automatically start when your server boots. If you're like me, that means that after rebooting your EC2 instance, you'll feel a moment of terror when FTP seems to be broken - but in reality, it's just not running!. Here's a handy way to fix that:
> sudo chkconfig --level 345 vsftpd on
Alternatively, if you are using redhat, another way to manage your services is by using this nifty graphic user interface to control which services should automatically start:
> sudo ntsysv
Now vsftpd will automatically start up when your server boots up.
Appendix B: Changing a user's FTP home directory
* NOTE: Iman Sedighi has posted a more elegant solution for restricting users access to a specific directory. Please refer to his excellent solution posted as an answer *
You might want to create a user and restrict their FTP access to a specific folder, such as /var/www. In order to do this, you'll need to change the user's default home directory:
> sudo usermod -d /var/www/ username
In this specific example, it's typical to give the user permissions to the 'www' group, which is often associated with the /var/www folder:
> sudo usermod -a -G www username
| https://stackoverflow.com//questions/7052875/setting-up-ftp-on-amazon-cloud-server |
linux - Finding Docker container processes? (from host point of view) | I am doing some tests on docker and containers and I was wondering: |
You can use docker top command.
This command lists all processes running within your container.
For instance this command on a single process container on my box displays:
UID PID PPID C STIME TTY TIME CMD
root 14097 13930 0 23:17 pts/6 00:00:00 /bin/bash
All methods mentioned by others are also possible to use but this one should be easiest.
Update:
To simply get the main process id within the container use this command:
docker inspect -f '{{.State.Pid}}' <container id>
| https://stackoverflow.com//questions/34878808/finding-docker-container-processes-from-host-point-of-view |
linux - tcp_tw_reuse vs tcp_tw_recycle : Which to use (or both)? | I have a website and application which use a significant number of connections. It normally has about 3,000 connections statically open, and can receive anywhere from 5,000 to 50,000 connection attempts in a few seconds time frame. |
According to Linux documentation, you should use the TCP_TW_REUSE flag to allow reusing sockets in TIME_WAIT state for new connections.
It seems to be a good option when dealing with a web server that have to handle many short TCP connections left in a TIME_WAIT state.
As described here, The TCP_TW_RECYCLE could cause some problems when using load balancers...
EDIT (to add some warnings ;) ):
as mentionned in comment by @raittes, the "problems when using load balancers" is about public-facing servers. When recycle is enabled, the server can't distinguish new incoming connections from different clients behind the same NAT device.
| https://stackoverflow.com//questions/6426253/tcp-tw-reuse-vs-tcp-tw-recycle-which-to-use-or-both |
JSON command line formatter tool for Linux | Want to improve this question? Update the question so it's on-topic for Stack Overflow. |
alias pp='python -mjson.tool'
pp mydata.json
From the first link in the accepted answer: http://ruslanspivak.com/2010/10/12/pretty-print-json-from-the-command-line/
| https://stackoverflow.com//questions/5243885/json-command-line-formatter-tool-for-linux |
c++ - How to fix: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.15' not found | So I'm now desperate in finding a fix for this. I'm compiling a shared library .so in Ubuntu 32 bit (Have tried doing it under Debian and Ubuntu 64 bit, but none worked either) |
Link statically to libstdc++ with -static-libstdc++ gcc option.
| https://stackoverflow.com//questions/19386651/how-to-fix-usr-lib-libstdc-so-6-version-glibcxx-3-4-15-not-found |
c++ - Finding current executable's path without /proc/self/exe | It seems to me that Linux has it easy with /proc/self/exe. But I'd like to know if there is a convenient way to find the current application's directory in C/C++ with cross-platform interfaces. I've seen some projects mucking around with argv[0], but it doesn't seem entirely reliable. |
Some OS-specific interfaces:
Mac OS X: _NSGetExecutablePath() (man 3 dyld)
Linux: readlink /proc/self/exe
Solaris: getexecname()
FreeBSD: sysctl CTL_KERN KERN_PROC KERN_PROC_PATHNAME -1
FreeBSD if it has procfs: readlink /proc/curproc/file (FreeBSD doesn't have procfs by default)
NetBSD: readlink /proc/curproc/exe
DragonFly BSD: readlink /proc/curproc/file
Windows: GetModuleFileName() with hModule = NULL
There are also third party libraries that can be used to get this information, such as whereami as mentioned in prideout's answer, or if you are using Qt, QCoreApplication::applicationFilePath() as mentioned in the comments.
The portable (but less reliable) method is to use argv[0]. Although it could be set to anything by the calling program, by convention it is set to either a path name of the executable or a name that was found using $PATH.
Some shells, including bash and ksh, set the environment variable "_" to the full path of the executable before it is executed. In that case you can use getenv("_") to get it. However this is unreliable because not all shells do this, and it could be set to anything or be left over from a parent process which did not change it before executing your program.
| https://stackoverflow.com//questions/1023306/finding-current-executables-path-without-proc-self-exe |
Locking Executing Files: Windows does, Linux doesn't. Why? | I noticed when a file is executed on Windows (.exe or .dll), it is locked and cannot be deleted, moved or modified. |
Linux has a reference-count mechanism, so you can delete the file while it is executing, and it will continue to exist as long as some process (Which previously opened it) has an open handle for it. The directory entry for the file is removed when you delete it, so it cannot be opened any more, but processes already using this file can still use it. Once all processes using this file terminate, the file is deleted automatically.
Windows does not have this capability, so it is forced to lock the file until all processes executing from it have finished.
I believe that the Linux behavior is preferable. There are probably some deep architectural reasons, but the prime (and simple) reason I find most compelling is that in Windows, you sometimes cannot delete a file, you have no idea why, and all you know is that some process is keeping it in use. In Linux it never happens.
| https://stackoverflow.com//questions/196897/locking-executing-files-windows-does-linux-doesnt-why |
python - How can I prevent Google Colab from disconnecting? | Is there a way to programmatically prevent Google Colab from disconnecting on a timeout? |
As of March 2021, none of these methods will work as Google added a CAPTCHA button that randomly pops up after some time.
Prior to that, the solution was very easy, and didn't need any JavaScript. Just create a new cell at the bottom having the following line:
while True:pass
Now keep the cell in the run sequence so that the infinite loop won't stop and thus keep your session alive.
Old method:
Set a JavaScript interval to click on the connect button every 60 seconds.
Open developer-settings (in your web-browser) with Ctrl+Shift+I then click on console tab and type this on the console prompt. (for mac press Option+Command+I)
function ConnectButton(){
console.log("Connect pushed");
document.querySelector("#top-toolbar > colab-connectbutton").shadowRoot.querySelector("#connect").click()
}
setInterval(ConnectButton,60000);
| https://stackoverflow.com//questions/57113226/how-can-i-prevent-google-colab-from-disconnecting |
linux - Is it better to use git grep than plain grep if we want to search in versioned source code? | In a git repository, is there any difference/benefit using git grep over good old grep?
An example would be? |
The two are very similar. The main difference is that git grep defaults to searching in the files that are tracked by git.
Examples
If I want to find foo within my project I can use git grep or good ol' stand-alone grep:
git grep foo
grep -R foo .
The git grep version will only search in files tracked by git, whereas the grep version will search everything in the directory. So far so similar; either one could be better depending on what you want to achieve.
What if we want to limit the search to only .rb files?
git grep foo -- *.rb
grep -R --include=*.rb foo .
The plain old grep version is getting a bit more wordy, but if you're used to using grep that may not be a problem. They're still not going to search exactly the same files, but again it depends on what you want to achieve.
What about searching in the previous version of the project?
git grep foo HEAD^
git checkout HEAD^; grep -R foo .; git checkout -
This is where git grep makes a real difference: You can search in another revision of the project without checking it out first. This isn't a situation that comes up too often for me though; I usually want to search in the version of the project I have checked out.
Configuring git grep
There are some git config variables that modify the behaviour of git grep and avoid the need to pass a couple of command line arguments:
grep.lineNumber: Always show line numbers of matches (you can pass -n to both grep and git grep to get this behaviour)
grep.extendedRegexp: Always use extended regular expressions (you can pass -E to both grep and git grep to get this behaviour)
In practice
In practice I have gg aliased to git grep -En, and this almost always does what I want.
| https://stackoverflow.com//questions/17557684/is-it-better-to-use-git-grep-than-plain-grep-if-we-want-to-search-in-versioned-s |
linux - How to set proxy for wget? | I want to download something with wget using a proxy: |
For all users of the system via the /etc/wgetrc or for the user only with the ~/.wgetrc file:
use_proxy=yes
http_proxy=127.0.0.1:8080
https_proxy=127.0.0.1:8080
or via -e options placed after the URL:
wget ... -e use_proxy=yes -e http_proxy=127.0.0.1:8080 ...
| https://stackoverflow.com//questions/11211705/how-to-set-proxy-for-wget |
Kill python interpeter in linux from the terminal | I want to kill python interpeter - The intention is that all the python files that are running in this moment will stop (without any informantion about this files).
obviously the processes should be closed. |
pkill -9 python
should kill any running python process.
| https://stackoverflow.com//questions/18428750/kill-python-interpeter-in-linux-from-the-terminal |
c++ - How do I install g++ for Fedora? | How do I install g++ for Fedora Linux? I have been searching the dnf command to install g++ but didn't find anything. |
The package you're looking for is confusingly named gcc-c++.
| https://stackoverflow.com//questions/12952913/how-do-i-install-g-for-fedora |
linux - How can I set an environment variable only for the duration of the script? | On Linux (Ubuntu 11.04 (Natty Narwhal)) in Bash, is it possible to temporarily set an environment variable that will only be different from the normal variable for the duration of the script? |
VAR1=value1 VAR2=value2 myScript args ...
| https://stackoverflow.com//questions/7128542/how-can-i-set-an-environment-variable-only-for-the-duration-of-the-script |
linux - make -j 8 g++: internal compiler error: Killed (program cc1plus) | When I deploy Apache Mesos on Ubuntu12.04, I follow the official document, in step "make -j 8" I'm getting this error in the console: |
Try running (just after the failure) dmesg.
Do you see a line like this?
Out of memory: Kill process 23747 (cc1plus) score 15 or sacrifice child
Killed process 23747, UID 2243, (cc1plus) total-vm:214456kB, anon-rss:178936kB, file-rss:5908kB
Most likely that is your problem. Running make -j 8 runs lots of process which use more memory. The problem above occurs when your system runs out of memory. In this case rather than the whole system falling over, the operating systems runs a process to score each process on the system. The one that scores the highest gets killed by the operating system to free up memory. If the process that is killed is cc1plus, gcc (perhaps incorrectly) interprets this as the process crashing and hence assumes that it must be a compiler bug. But it isn't really, the problem is the OS killed cc1plus, rather than it crashed.
If this is the case, you are running out of memory. So run perhaps make -j 4 instead. This will mean fewer parallel jobs and will mean the compilation will take longer but hopefully will not exhaust your system memory.
| https://stackoverflow.com//questions/30887143/make-j-8-g-internal-compiler-error-killed-program-cc1plus |
linux - nginx not listening to port 80 | I've just installed a Ubuntu 12.04 server and nginx 1.2.7, removed default from sites-enabled and added my own file into sites-available and symlink at sites-enabled. Then restarted nginx. |
I had this same problem, the solution was that I had not symlinked my siteconf file correctly. Try running vim /etc/nginx/sites-enabled/mysite.com—can you get to it? I was getting "Permission Denied."
If not run:
rm /etc/nginx/sites-enabled/mysite.com
ln -s /etc/nginx/sites-available/mysite.com /etc/nginx/sites-enabled/mysite.com
| https://stackoverflow.com//questions/16021481/nginx-not-listening-to-port-80 |
multithreading - How can I monitor the thread count of a process on linux? | I would like to monitor the number of threads used by a specific process on Linux.
Is there an easy way to get this information without impacting the performance of the process? |
try
ps huH p <PID_OF_U_PROCESS> | wc -l
or htop
| https://stackoverflow.com//questions/268680/how-can-i-monitor-the-thread-count-of-a-process-on-linux |
linux - How to concatenate two strings to build a complete path | I am trying to write a bash script. In this script I want user to enter a path of a directory. Then I want to append some strings at the end of this string and build a path to some subdirectories.
For example assume user enters an string like this: |
The POSIX standard mandates that multiple / are treated as a single / in a file name. Thus
//dir///subdir////file is the same as /dir/subdir/file.
As such concatenating a two strings to build a complete path is a simple as:
full_path="$part1/$part2"
| https://stackoverflow.com//questions/11226322/how-to-concatenate-two-strings-to-build-a-complete-path |
linux - When grep "\\" XXFile I got "Trailing Backslash" | Now I want to find whether there are lines containing '\' character. I tried grep "\\" XXFile but it hints "Trailing Backslash". But when I tried grep '\\' XXFile it is OK. Could anyone explain why the first case cannot run? Thanks. |
The difference is in how the shell treats the backslashes:
When you write "\\" in double quotes, the shell interprets the backslash escape and ends up passing the string \ to grep. Grep then sees a backslash with no following character, so it emits a "trailing backslash" warning. If you want to use double quotes you need to apply two levels of escaping, one for the shell and one for grep. The result: "\\\\".
When you write '\\' in single quotes, the shell does not do any interpretation, which means grep receives the string \\ with both backslashes intact. Grep interprets this as an escaped backslash, so it searches the file for a literal backslash character.
If that's not clear, we can use echo to see exactly what the shell is doing. echo doesn't do any backslash interpretation itself, so what it prints is what the shell passed to it.
$ echo "\\"
\
$ echo '\\'
\\
| https://stackoverflow.com//questions/20342464/when-grep-xxfile-i-got-trailing-backslash |
linux - how to find the target file's full(absolute path) of the symbolic link or soft link in python | when i give
ls -l /etc/fonts/conf.d/70-yes-bitmaps.conf |
os.path.realpath(path)
os.path.realpath returns the canonical path of the specified filename, eliminating any symbolic links encountered in the path.
| https://stackoverflow.com//questions/3220755/how-to-find-the-target-files-fullabsolute-path-of-the-symbolic-link-or-soft-l |
linux - rsync - mkstemp failed: Permission denied (13) | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
Make sure the user you're rsync'd into on the remote machine has write access to the contents of the folder AND the folder itself, as rsync tried to update the modification time on the folder itself.
| https://stackoverflow.com//questions/11039559/rsync-mkstemp-failed-permission-denied-13 |
linux - sh: 0: getcwd() failed: No such file or directory on cited drive | I am trying to compile ARM code on Ubuntu 12.04 (Precise Pangolin). |
This error is usually caused by running a command from a directory that no longer exists.
Try changing your directory and rerun the command.
| https://stackoverflow.com//questions/12758125/sh-0-getcwd-failed-no-such-file-or-directory-on-cited-drive |
linux - how to find the target file's full(absolute path) of the symbolic link or soft link in python | when i give
ls -l /etc/fonts/conf.d/70-yes-bitmaps.conf |
os.path.realpath(path)
os.path.realpath returns the canonical path of the specified filename, eliminating any symbolic links encountered in the path.
| https://stackoverflow.com//questions/3220755/how-to-find-the-target-files-fullabsolute-path-of-the-symbolic-link-or-soft-l |
c - Undefined reference to pthread_create in Linux | I picked up the following demo off the web from https://computing.llnl.gov/tutorials/pthreads/ |
For Linux the correct command is:
gcc -pthread -o term term.c
In general, libraries should follow sources and objects on command line, and -lpthread is not an "option", it's a library specification. On a system with only libpthread.a installed,
gcc -lpthread ...
will fail to link.
Read this or this detailed explanation.
| https://stackoverflow.com//questions/1662909/undefined-reference-to-pthread-create-in-linux |
linux - Debugging crontab jobs | I have added a crontab entry on a Linux server that will run a Java executable. The Java code uses its own class for logging errors and messages into a log file. |
You can enable logging for cron jobs in order to track problems. You need to edit the /etc/rsyslog.conf or /etc/rsyslog.d/50-default.conf (on Ubuntu) file and make sure you have the following line uncommented or add it if it is missing:
cron.* /var/log/cron.log
Then restart rsyslog and cron:
sudo service rsyslog restart
sudo service cron restart
Cron jobs will log to /var/log/cron.log.
| https://stackoverflow.com//questions/4883069/debugging-crontab-jobs |
linux - Explain the effects of export LANG, LC_CTYPE, and LC_ALL | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
I'll explain with detail:
export LANG=ru_RU.UTF-8
That is a shell command that will export an environment variable named LANG with the given value ru_RU.UTF-8. That instructs internationalized programs to use the Russian language (ru), variant from Russia (RU), and the UTF-8 encoding for console output.
Generally this single line is enough.
This other one:
export LC_CTYPE=ru_RU.UTF-8
Does a similar thing, but it tells the program not to change the language, but only the CTYPE to Russian. If a program can change a text to uppercase, then it will use the Russian rules to do so, even though the text itself may be in English.
It is worth saying that mixing LANG and LC_CTYPE can give unexpected results, because few people do that, so it is quite untested, unless maybe:
export LANG=ru_RU.UTF-8
export LC_CTYPE=C
That will make the program output in Russian, but the CTYPE standard old C style.
The last line, LC_ALL is a last resort override, that will make the program ignore all the other LC_* variables and use this. I think that you should never write it in a profile line, but use it to run a program in a given language. For example, if you want to write a bug report, and you don't want any kind of localized output, and you don't know which LC_* variables are set:
LC_ALL=C program
About changing the language of all your programs or only the console, that depends on where you put these lines. I put mine in ~/.bashrc so they don't apply to the GUI, only to the bash consoles.
| https://stackoverflow.com//questions/30479607/explain-the-effects-of-export-lang-lc-ctype-and-lc-all |
linux - Rename all files in a folder with a prefix in a single command | Rename all the files within a folder with prefix "Unix_" |
If your filenames contain no whitepace and you don't have any subdirectories, you can use a simple for loop:
$ for FILENAME in *; do mv $FILENAME Unix_$FILENAME; done
Otherwise use the convenient rename command (which is a perl script) - although it might not be available out of the box on every Unix (e.g. OS X doesn't come with rename).
A short overview at debian-administration.org:
Easily renaming multiple files
If your filenames contain whitespace it's easier to use find, on Linux the following should work:
$ find . -type f -name '*' -printf "echo mv '%h/%f' '%h/Unix_%f\n'" | sh
On BSD systems, there is no -printf option, unfortunately. But GNU findutils should be installable (on e.g. Mac OS X with brew install findutils).
$ gfind . -type f -name '*' -printf "mv \"%h/%f\" \"%h/Unix_%f\"\n" | sh
| https://stackoverflow.com//questions/6329505/rename-all-files-in-a-folder-with-a-prefix-in-a-single-command |
How is the Linux kernel tested? | How do the Linux kernel developers test their code locally and after they have it committed? Do they use some kind of unit testing and build automation? Test plans? |
The Linux kernel has a heavy emphasis on community testing.
Typically, any developer will test their own code before submitting, and quite often they will be using a development version of the kernel from Linus, or one of the other unstable/development trees for a project relevant to their work. This means they are often testing both their changes and other people's changes.
There tends not to be much in the way of formal test plans, but extra testing may be asked for before features are merged into upstream trees.
As Dean pointed out, there's also some automated testing: The Linux Test Project and the kernel Autotest (good overview).
Developers will often also write automated tests targeted to test their change, but I'm not sure there's a (often used) mechanism to centrally collect these ad hoc tests.
It depends a lot on which area of the kernel is being changed of course - the testing you'd do for a new network driver is quite different to the testing you'd do when replacing the core scheduling algorithm.
| https://stackoverflow.com//questions/3177338/how-is-the-linux-kernel-tested |
linux - How can I open some ports on Ubuntu? | I know a little about Linux. Today I created a VPN server on my Ubuntu installation according to Set up a simple IPsec/L2TP VPN server for Ubuntu, Arch Linux and Debian. |
Ubuntu these days comes with UFW - Uncomplicated Firewall. UFW is an easy-to-use method of handling iptables rules.
Try using this command to allow a port:
sudo ufw allow 1701
To test connectivity, you could try shutting down the VPN software (freeing up the ports) and using netcat to listen, like this:
nc -l 1701
Then use telnet from your Windows host and see what shows up on your Ubuntu terminal. This can be repeated for each port you'd like to test.
| https://stackoverflow.com//questions/30251889/how-can-i-open-some-ports-on-ubuntu |
java - Detecting Windows or Linux? | I am seeking to run a common Java program in both Windows and Linux. |
apache commons lang has a class SystemUtils.java
you can use :
SystemUtils.IS_OS_LINUX
SystemUtils.IS_OS_WINDOWS
| https://stackoverflow.com//questions/14288185/detecting-windows-or-linux |
linux - couldn't connect to server 127.0.0.1 shell/mongo.js | when i setup mongodb in my ubuntu , i try : ./mongo it show this error : |
Manually remove the lockfile: sudo rm /var/lib/mongodb/mongod.lock
Run the repair script: sudo -u mongodb mongod -f /etc/mongodb.conf --repair
Please note the following:
You must run this command as the mongodb user. If you run it as root,
then root will own files in /var/lib/mongodb/ that are necessary to
run the mongodb daemon and therefore when the daemon trys to run
later as the mongodb user, it won't have permissions to start. In
that case you'll get this error: Unable to create / open lock file
for lockfilepath: /var/lib/mongodb/mongod.lock errno:13 Permission
denied, terminating.
On Ubuntu, you must specify the configuration file /etc/mongodb.conf
using the -f flag. Otherwise it will look for the data files in the
wrong place and you will see the following error: dbpath (/data/db/)
does not exist, terminating.
| https://stackoverflow.com//questions/5726032/couldnt-connect-to-server-127-0-0-1-shell-mongo-js |
linux - What's the difference between .so, .la and .a library files? | I know an .so file is a kind of dynamic library (lots of threads can share such libraries so there is no need to have more than one copy of it in memory). But what is the difference between .a and .la? Are these all static libraries? |
File type breakdown
.so files are dynamic libraries. The suffix stands for "shared object", because all the applications that are linked with the library use the same file, rather than making a copy in the resulting executable.
.a files are static libraries. The suffix stands for "archive", because they're actually just an archive (made with the ar command -- a predecessor of tar that's now just used for making libraries) of the original .o object files.
.la files are text files used by the GNU "libtools" package to describe the files that make up the corresponding library. You can find more information about them in this question: What are libtool's .la file for?
Static vs Dynamic
Static
Pro: The user always uses the version of the library that you've tested with your application, so there shouldn't be any surprising compatibility problems.
Con: If a problem is fixed in a library, you need to redistribute your application to take advantage of it. However, unless it's a library that users are likely to update on their own, you'd might need to do this anyway.
Dynamic
Pro: Your process's memory footprint is smaller, because the memory used for the library is amortized among all the processes using the library.
Pro: Libraries can be loaded on demand at run time; this is good for plugins, so you don't have to choose the plugins to be used when compiling and installing the software. New plugins can be added on the fly.
Con: The library might not exist on the system where someone is trying to install the application, or they might have a version that's not compatible with the application. To mitigate this, the application package might need to include a copy of the library, so it can install it if necessary. This is also often mitigated by package managers, which can download and install any necessary dependencies.
Con: Link-Time Optimization is generally not possible, so there could possibly be efficiency implications in high-performance applications. See the Wikipedia discussion of WPO and LTO.
Dynamic libraries are especially useful for system libraries, like libc. These libraries often need to include code that's dependent on the specific OS and version, because kernel interfaces have changed. If you link a program with a static system library, it will only run on the version of the OS that this library version was written for. But if you use a dynamic library, it will automatically pick up the library that's installed on the system you run on.
| https://stackoverflow.com//questions/12237282/whats-the-difference-between-so-la-and-a-library-files |
linux - /bin/sh: pushd: not found | I am doing the following inside a make file |
pushd is a bash enhancement to the POSIX-specified Bourne Shell. pushd cannot be easily implemented as a command, because the current working directory is a feature of a process that cannot be changed by child processes. (A hypothetical pushd command might do the chdir(2) call and then start a new shell, but ... it wouldn't be very usable.) pushd is a shell builtin, just like cd.
So, either change your script to start with #!/bin/bash or store the current working directory in a variable, do your work, then change back. Depends if you want a shell script that works on very reduced systems (say, a Debian build server) or if you're fine always requiring bash.
| https://stackoverflow.com//questions/5193048/bin-sh-pushd-not-found |
What is a good easy to use profiler for C++ on Linux? | Questions asking us to recommend or find a tool, library or favorite off-site resource are off-topic for Stack Overflow as they tend to attract opinionated answers and spam. Instead, describe the problem and what has been done so far to solve it. |
Use gprof.
Just compile with -pg flag (I think (but am not sure) you have to turn of optimizations though.) and use gprof to analyze the gmon.out file that your executable will then produce.
eg:
gcc -pg -o whatever whatever.c
./whatever
gprof whatever gmon.out
Same thing with g++ and cpp.
| https://stackoverflow.com//questions/1168766/what-is-a-good-easy-to-use-profiler-for-c-on-linux |
c - Difference between "system" and "exec" in Linux? | What is the difference between system and exec family commands? Especially I want to know which one of them creates child process to work? |
system() calls out to sh to handle your command line, so you can get wildcard expansion, etc. exec() and its friends replace the current process image with a new process image.
With system(), your program continues running and you get back some status about the external command you called. With exec(), your process is obliterated.
In general, I guess you could think of system() as a higher-level interface. You could duplicate its functionality yourself using some combination fork(), exec(), and wait().
To answer your final question, system() causes a child process to be created, and the exec() family do not. You would need to use fork() for that.
| https://stackoverflow.com//questions/1697440/difference-between-system-and-exec-in-linux |
linux - Debugging crontab jobs | I have added a crontab entry on a Linux server that will run a Java executable. The Java code uses its own class for logging errors and messages into a log file. |
You can enable logging for cron jobs in order to track problems. You need to edit the /etc/rsyslog.conf or /etc/rsyslog.d/50-default.conf (on Ubuntu) file and make sure you have the following line uncommented or add it if it is missing:
cron.* /var/log/cron.log
Then restart rsyslog and cron:
sudo service rsyslog restart
sudo service cron restart
Cron jobs will log to /var/log/cron.log.
| https://stackoverflow.com//questions/4883069/debugging-crontab-jobs |
c - Writing programs to cope with I/O errors causing lost writes on Linux | TL;DR: If the Linux kernel loses a buffered I/O write, is there any way for the application to find out? |
fsync() returns -EIO if the kernel lost a write
(Note: early part references older kernels; updated below to reflect modern kernels)
It looks like async buffer write-out in end_buffer_async_write(...) failures set an -EIO flag on the failed dirty buffer page for the file:
set_bit(AS_EIO, &page->mapping->flags);
set_buffer_write_io_error(bh);
clear_buffer_uptodate(bh);
SetPageError(page);
which is then detected by wait_on_page_writeback_range(...) as called by do_sync_mapping_range(...) as called by sys_sync_file_range(...) as called by sys_sync_file_range2(...) to implement the C library call fsync().
But only once!
This comment on sys_sync_file_range
168 * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any
169 * I/O errors or ENOSPC conditions and will return those to the caller, after
170 * clearing the EIO and ENOSPC flags in the address_space.
suggests that when fsync() returns -EIO or (undocumented in the manpage) -ENOSPC, it will clear the error state so a subsequent fsync() will report success even though the pages never got written.
Sure enough wait_on_page_writeback_range(...) clears the error bits when it tests them:
301 /* Check for outstanding write errors */
302 if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
303 ret = -ENOSPC;
304 if (test_and_clear_bit(AS_EIO, &mapping->flags))
305 ret = -EIO;
So if the application expects it can re-try fsync() until it succeeds and trust that the data is on-disk, it is terribly wrong.
I'm pretty sure this is the source of the data corruption I found in the DBMS. It retries fsync() and thinks all will be well when it succeeds.
Is this allowed?
The POSIX/SuS docs on fsync() don't really specify this either way:
If the fsync() function fails, outstanding I/O operations are not guaranteed to have been completed.
Linux's man-page for fsync() just doesn't say anything about what happens on failure.
So it seems that the meaning of fsync() errors is "I don't know what happened to your writes, might've worked or not, better try again to be sure".
Newer kernels
On 4.9 end_buffer_async_write sets -EIO on the page, just via mapping_set_error.
buffer_io_error(bh, ", lost async page write");
mapping_set_error(page->mapping, -EIO);
set_buffer_write_io_error(bh);
clear_buffer_uptodate(bh);
SetPageError(page);
On the sync side I think it's similar, though the structure is now pretty complex to follow. filemap_check_errors in mm/filemap.c now does:
if (test_bit(AS_EIO, &mapping->flags) &&
test_and_clear_bit(AS_EIO, &mapping->flags))
ret = -EIO;
which has much the same effect. Error checks seem to all go through filemap_check_errors which does a test-and-clear:
if (test_bit(AS_EIO, &mapping->flags) &&
test_and_clear_bit(AS_EIO, &mapping->flags))
ret = -EIO;
return ret;
I'm using btrfs on my laptop, but when I create an ext4 loopback for testing on /mnt/tmp and set up a perf probe on it:
sudo dd if=/dev/zero of=/tmp/ext bs=1M count=100
sudo mke2fs -j -T ext4 /tmp/ext
sudo mount -o loop /tmp/ext /mnt/tmp
sudo perf probe filemap_check_errors
sudo perf record -g -e probe:end_buffer_async_write -e probe:filemap_check_errors dd if=/dev/zero of=/mnt/tmp/test bs=4k count=1 conv=fsync
I find the following call stack in perf report -T:
---__GI___libc_fsync
entry_SYSCALL_64_fastpath
sys_fsync
do_fsync
vfs_fsync_range
ext4_sync_file
filemap_write_and_wait_range
filemap_check_errors
A read-through suggests that yeah, modern kernels behave the same.
This seems to mean that if fsync() (or presumably write() or close()) returns -EIO, the file is in some undefined state between when you last successfully fsync()d or close()d it and its most recently write()ten state.
Test
I've implemented a test case to demonstrate this behaviour.
Implications
A DBMS can cope with this by entering crash recovery. How on earth is a normal user application supposed to cope with this? The fsync() man page gives no warning that it means "fsync-if-you-feel-like-it" and I expect a lot of apps won't cope well with this behaviour.
Bug reports
https://bugzilla.kernel.org/show_bug.cgi?id=194755
https://bugzilla.kernel.org/show_bug.cgi?id=194757
Further reading
lwn.net touched on this in the article "Improved block-layer error handling".
postgresql.org mailing list thread.
| https://stackoverflow.com//questions/42434872/writing-programs-to-cope-with-i-o-errors-causing-lost-writes-on-linux |
linux - how to detect invalid utf8 unicode/binary in a text file | I need to detect corrupted text file where there are invalid (non-ASCII) utf-8, Unicode or binary characters. |
Assuming you have your locale set to UTF-8 (see locale output), this works well to recognize invalid UTF-8 sequences:
grep -axv '.*' file.txt
Explanation (from grep man page):
-a, --text: treats file as text, essential prevents grep to abort once finding an invalid byte sequence (not being utf8)
-v, --invert-match: inverts the output showing lines not matched
-x '.*' (--line-regexp): means to match a complete line consisting of any utf8 character.
Hence, there will be output, which is the lines containing the invalid not utf8 byte sequence containing lines (since inverted -v)
| https://stackoverflow.com//questions/29465612/how-to-detect-invalid-utf8-unicode-binary-in-a-text-file |
linux - How to check existence of a folder with python and then remove it? | I want to remove dataset folder from dataset3 folder. But the following code is not removing dataset.
First I want to check if dataset already exist in dataset then remove dataset.
Can some one please point out my mistake in following code? |
Python's os.rmdir() only works on empty the directories, however shutil.rmtree() doesn't care (even if there are subdirectories) which makes it very similar to the Linux rm -rf command.
import os
import shutil
dirpath = os.path.join('dataset3', 'dataset')
if os.path.exists(dirpath) and os.path.isdir(dirpath):
shutil.rmtree(dirpath)
Modern approach
In Python 3.4+ you can do same thing using the pathlib module to make the code more object-oriented and readable:
from pathlib import Path
import shutil
dirpath = Path('dataset3') / 'dataset'
if dirpath.exists() and dirpath.is_dir():
shutil.rmtree(dirpath)
| https://stackoverflow.com//questions/43765117/how-to-check-existence-of-a-folder-with-python-and-then-remove-it |
linux - rsync - mkstemp failed: Permission denied (13) | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
Make sure the user you're rsync'd into on the remote machine has write access to the contents of the folder AND the folder itself, as rsync tried to update the modification time on the folder itself.
| https://stackoverflow.com//questions/11039559/rsync-mkstemp-failed-permission-denied-13 |
JSON command line formatter tool for Linux | Want to improve this question? Update the question so it's on-topic for Stack Overflow. |
alias pp='python -mjson.tool'
pp mydata.json
From the first link in the accepted answer: http://ruslanspivak.com/2010/10/12/pretty-print-json-from-the-command-line/
| https://stackoverflow.com//questions/5243885/json-command-line-formatter-tool-for-linux |
linux - mysql_config not found when installing mysqldb python interface | I am trying to get a Python script to run on the linux server I'm connected to via ssh. The script uses mysqldb. I have all the other components I need, but when I try to install mySQLdb via setuptools like so:, |
mySQLdb is a python interface for mysql, but it is not mysql itself. And apparently mySQLdb needs the command 'mysql_config', so you need to install that first.
Can you confirm that you did or did not install mysql itself, by running "mysql" from the shell? That should give you a response other than "mysql: command not found".
Which linux distribution are you using? Mysql is pre-packaged for most linux distributions. For example, for debian / ubuntu, installing mysql is as easy as
sudo apt-get install mysql-server
mysql-config is in a different package, which can be installed from (again, assuming debian / ubuntu):
sudo apt-get install libmysqlclient-dev
if you are using mariadb, the drop in replacement for mysql, then run
sudo apt-get install libmariadbclient-dev
Reference:
https://github.com/JudgeGirl/Judge-sender/issues/4#issuecomment-186542797
| https://stackoverflow.com//questions/7475223/mysql-config-not-found-when-installing-mysqldb-python-interface |
linux - Use sudo with password as parameter | Want to improve this question? Update the question so it's on-topic for Stack Overflow. |
The -S switch makes sudo read the password from STDIN. This means you can do
echo mypassword | sudo -S command
to pass the password to sudo
However, the suggestions by others that do not involve passing the password as part of a command such as checking if the user is root are probably much better ideas for security reasons
| https://stackoverflow.com//questions/11955298/use-sudo-with-password-as-parameter |
c - error: Libtool library used but 'LIBTOOL' is undefined | I am trying to automake the OrientDb C++ library, but getting some errors. |
A good answer for me was to install libtool:
sudo apt-get install libtool
| https://stackoverflow.com//questions/18978252/error-libtool-library-used-but-libtool-is-undefined |
linux - When should we use mutex and when should we use semaphore | When should we use mutex and when should we use semaphore ? |
Here is how I remember when to use what -
Semaphore:
Use a semaphore when you (thread) want to sleep till some other thread tells you to wake up. Semaphore 'down' happens in one thread (producer) and semaphore 'up' (for same semaphore) happens in another thread (consumer)
e.g.: In producer-consumer problem, producer wants to sleep till at least one buffer slot is empty - only the consumer thread can tell when a buffer slot is empty.
Mutex:
Use a mutex when you (thread) want to execute code that should not be executed by any other thread at the same time. Mutex 'down' happens in one thread and mutex 'up' must happen in the same thread later on.
e.g.: If you are deleting a node from a global linked list, you do not want another thread to muck around with pointers while you are deleting the node. When you acquire a mutex and are busy deleting a node, if another thread tries to acquire the same mutex, it will be put to sleep till you release the mutex.
Spinlock:
Use a spinlock when you really want to use a mutex but your thread is not allowed to sleep.
e.g.: An interrupt handler within OS kernel must never sleep. If it does the system will freeze / crash. If you need to insert a node to globally shared linked list from the interrupt handler, acquire a spinlock - insert node - release spinlock.
| https://stackoverflow.com//questions/4039899/when-should-we-use-mutex-and-when-should-we-use-semaphore |
c - How to capture Control+D signal? | I want to capture the Ctrl+D signal in my program and write a signal handler for it.
How can I do that?
I am working on C and using a Linux system. |
As others have already said, to handle Control+D, handle "end of file"s.
Control+D is a piece of communication between the user and the pseudo-file that you see as stdin. It does not mean specifically "end of file", but more generally "flush the input I typed so far". Flushing means that any read() call on stdin in your program returns with the length of the input typed since the last flush. If the line is nonempty, the input becomes available to your program although the user did not type "return" yet. If the line is empty, then read() returns with zero, and that is interpreted as "end of file".
So when using Control+D to end a program, it only works at the beginning of a line, or if you do it twice (first time to flush, second time for read() to return zero).
Try it:
$ cat
foo
(type Control-D once)
foofoo (read has returned "foo")
(type Control-D again)
$
| https://stackoverflow.com//questions/1516122/how-to-capture-controld-signal |
linux - How to create a hex dump of file containing only the hex characters without spaces in bash? | How do I create an unmodified hex dump of a binary file in Linux using bash? The od and hexdump commands both insert spaces in the dump and this is not ideal. |
xxd -p file
Or if you want it all on a single line:
xxd -p file | tr -d '\n'
| https://stackoverflow.com//questions/2614764/how-to-create-a-hex-dump-of-file-containing-only-the-hex-characters-without-spac |
linux - How to fix 'sudo: no tty present and no askpass program specified' error? | I am trying to compile some sources using a makefile. In the makefile there is a bunch of commands that need to be ran as sudo. |
Granting the user to use that command without prompting for password should resolve the problem. First open a shell console and type:
sudo visudo
Then edit that file to add to the very end:
username ALL = NOPASSWD: /fullpath/to/command, /fullpath/to/othercommand
eg
john ALL = NOPASSWD: /sbin/poweroff, /sbin/start, /sbin/stop
will allow user john to sudo poweroff, start and stop without being prompted for password.
Look at the bottom of the screen for the keystrokes you need to use in visudo - this is not vi by the way - and exit without saving at the first sign of any problem. Health warning: corrupting this file will have serious consequences, edit with care!
| https://stackoverflow.com//questions/21659637/how-to-fix-sudo-no-tty-present-and-no-askpass-program-specified-error |
scp from Linux to Windows | This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered. |
This one worked for me.
scp /home/ubuntu/myfile username@IP_of_windows_machine:/C:/Users/Anshul/Desktop
| https://stackoverflow.com//questions/10235778/scp-from-linux-to-windows |
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