neulab/tldr huggingface dataset:
This means that if you have a data-dependent problem you will probably have to do a lot of testing to find it.  If you are lucky, you may manage to find a file that either can't be sent across your network or that takes much longer to transfer than other similar length files.  You can then examine this file for repeated patterns that you can test using the -p option of ping.
The TTL value of an IP packet represents the maximum number of IP routers that the packet can go through before being thrown away.  In current practice you can expect each router in the Internet to decrement the TTL field by exactly one.
The TCP/IP specification states that the TTL field for TCP packets should be set to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2 used 15).
The maximum possible value of this field is 255, and most Unix systems set the TTL field of ICMP ECHO_REQUEST packets to 255.  This is why you will find you can ``ping'' some hosts, but not reach them with telnet(1) or ftp(1).
In normal operation ping prints the TTL value from the packet it receives.  When a remote system receives a ping packet, it can do one of three things with the TTL field in its response:
• Not change it; this is what Berkeley Unix systems did before the 4.3BSD Tahoe release. In this case the TTL value in the received packet will be 255 minus the number of routers in the round-trip path.
• Set it to 255; this is what current Berkeley Unix systems do.  In this case the TTL value in the received packet will be 255 minus the number of routers in the path from the remote system to the pinging host.
• Set it to some other value. Some machines use the same value for ICMP packets that they use for TCP packets, for example either 30 or 60. Others may use completely wild values.
• Many Hosts and Gateways ignore the RECORD_ROUTE option.
• The maximum IP header length is too small for options like RECORD_ROUTE to be completely useful.  There's not much that can be done about this, however.
• Flood pinging is not recommended in general, and flood pinging the broadcast address should only be done under very controlled conditions.
netstat(1), ifconfig(8).
The ping command appeared in 4.3BSD.
The version described here is its descendant specific to Linux.
ping requires CAP_NET_RAW capability to be executed. It may be used as set-uid root.
ping is part of iputils package and the latest versions are available in source form at ⟨http://www.skbuff.net/iputils/iputils-current.tar.bz2⟩.
A2ENMOD(8)                   System Manager's Manual                  A2ENMOD(8)
a2enmod, a2dismod - enable or disable an apache2 module
a2enmod [-q|--quiet] [-m|--maintmode] [ module ]
a2dismod [-q|--quiet] [-f|--force] [-m|--maintmode] [-p|--purge] [ module ]
This manual page documents briefly the a2enmod and a2dismod commands.
a2enmod is a script that enables the specified module within the apache2 configuration.  It does this by creating symlinks within /etc/apache2/mods-enabled.  Likewise, a2dismod disables a module by removing those symlinks.  It is not an error to enable a module which is already enabled, or to disable one which is already disabled.
Note that many modules have, in addition to a .load file, an associated .conf file.  Enabling the module puts the configuration directives in the .conf file as directives into the main server context of apache2.
-f, --force When disabling a module, also cascade disables all modules that depends on it.
a2enmod and a2dismod exit with status 0 if all modules are processed successfully, 1 if errors occur, 2 if an invalid option was used.
a2enmod imagemap a2dismod mime_magic
Enables the mod_imagemap module, and disables the mod_mime_magic module.
/etc/apache2/mods-available Directory with files giving information on available modules.
/etc/apache2/mods-enabled Directory with links to the files in mods-available for enabled modules.
apache2ctl(8), a2enconf(8), a2disconf(8), a2ensite(8), a2dissite(8).
This manual page was written by Daniel Stone <daniel@sfarc.net> for the Debian GNU/Linux distribution, as it is a Debian-specific script with the package.
ARPING(8)                            iputils                           ARPING(8)
arping - send ARP REQUEST to a neighbour host
arping [-AbDfhqUV] [-c count] [-w deadline] [-i interval] [-s source] [-I interface] {destination}
Ping destination on device interface by ARP packets, using source address source.
-A The same as -U, but ARP REPLY packets used instead of ARP REQUEST.
-b Send only MAC level broadcasts. Normally arping starts from sending broadcast, and switch to unicast after reply received.
-c count Stop after sending count ARP REQUEST packets. With deadline option, instead wait for count ARP REPLY packets, or until the timeout expires.
-D Duplicate address detection mode (DAD). See RFC2131, 4.4.1. Returns 0, if DAD succeeded i.e. no replies are received.
-f Finish after the first reply confirming that target is alive.
-I interface Name of network device where to send ARP REQUEST packets.
-h Print help page and exit.
-q Quiet output. Nothing is displayed.
-s source IP source address to use in ARP packets. If this option is absent, source address is:
• In DAD mode (with option -D) set to 0.0.0.0.
• In Unsolicited ARP mode (with options -U or -A) set to destination.
• Otherwise, it is calculated from routing tables.
-U Unsolicited ARP mode to update neighbours' ARP caches. No replies are expected.
-V Print version of the program and exit.
-w deadline Specify a timeout, in seconds, before arping exits regardless of how many packets have been sent or received. In this case arping does not stop after count packet are sent, it waits either for deadline expire or until count probes are answered.
-i interval Specify an interval, in seconds, between packets.
ping(8), clockdiff(8), tracepath(8).
arping was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.
arping requires CAP_NET_RAW capability to be executed. It is not recommended to be used as set-uid root, because it allows user to modify ARP caches of neighbour hosts.
arping is part of iputils package.
AC(1)                        General Commands Manual                       AC(1)
ac -  print statistics about users' connect time
ac     [ -d | --daily-totals ] [ -y | --print-year ] [ -p | --individual-totals ] [ people ] [ -f | --file filename ] [ -a | --all-days ] [ --complain ] [ --reboots ] [ --supplants ] [ --timewarps ] [ --compatibility ] [ --tw-leniency num ] [ --tw-suspicious num ] [ -z | --print-zeros ] [ --debug ] [ -V | --version ] [ -h | --help ]
ac prints out a report of connect time (in hours) based on the logins/logouts in the current wtmp file.  A total is also printed out.
The accounting file wtmp is maintained by init(8) and login(1).  Neither ac nor login creates the wtmp if it doesn't exist, no accounting is done. To begin accounting, create the file with a length of zero.
NOTE:  The wtmp file can get really big, really fast.  You might want to trim it every once and a while.
GNU ac works nearly the same UNIX ac, though it's a little smarter in several ways.  You should therefore expect differences in the output of GNU ac and the output of ac's on other systems.  Use the command info accounting to get additional information.
login(1), wtmp(5), init(8), sa(8)
scala(1)                          USER COMMANDS                         scala(1)
scala - Run code in the Scala 2 language
scala  [ <option> ]... [ <torun> <argument>... ]
<compiler-option> Any scalac option.  See scalac(1).
-howtorun:<how> How to execute <torun>, if it is present. Options for <how> are guess (the default), script, jar, and object.
-i <file> Requests that a file be pre-loaded.  It is only meaningful for interactive shells.
-e <string> Requests that its argument be executed as Scala code.
-savecompiled Save this compiled version of scripts in order to speed up later executions of the same script.  When running a script, save the compiled version in a file with the same name as the script but with an extension of .jar.  On subsequent runs of the same script, the pre-compiled .jar file will be used if it is newer than the script file.
-nocompdaemon Do not use the fsc offline compiler.
-nc    Same as -nocompdaemon.
-Dproperty=value Set a Java system property.  If no value is specified, then the property is set to the empty string.
<torun> A top-level object or a script file to run.
<argument> An arguments to pass to <torun>.
The scala utility runs Scala code using a Java runtime environment.  The Scala code to run is specified in one of three ways:
1.  With no arguments specified, a Scala shell starts and reads commands interactively.
2.  With -howtorun:object specified, the fully qualified name of a top-level Scala object may be specified.  The object should previously have been compiled using scalac(1).
3.  With -howtorun:script specified, a file containing Scala code may be specified.
If -howtorun: is left as the default (guess), then the scala command will check whether a file of the specified name exists.  If it does, then it will treat it as a script file; if it does not, then it will treat it as the name of an object.
In all three cases, arbitrary scalac options may be specified. The most common option is to specify a classpath with -classpath, but see the scalac(1) page for full details.
If an object is specified to run, then that object must be a top-level Scala object with the specified name.  The object must define a method main with the following signature:
def main(args: Array[String]): Unit
The method must return a Unit value, and it must accept a String array as a parameter.  All arguments specified on the command line will be passed as arguments to the main method.
If a script file is specified to run, then the file is read and all Scala statements and declarations in the file are processed in order. Any arguments specified will be available via the argsvariable.
Script files may have an optional header that is ignored if present. There are two ways to format the header: either beginning with #! and ending with !#, or beginning with ::#! and ending with ::!#.
Such a header must have each header boundary start at the beginning of a line.  Headers can be used to make stand-alone script files, as shown in the examples below.
When running a script or using -e, an already running compilation daemon (fsc) is used, or a new one started on demand.  The -nocompdaemon or -nc option can be used to prevent this.
If scala is run from an sbaz(1) directory, then it will add to its classpath any jars installed in the lib directory of the sbaz directory. Additionally, if no -classpath option is specified, then scala will add ".", the current directory, to the end of the classpath.
If any compiler options are specified, they must be first in the command line and must be followed by a bare hypen ("-") character. If no arguments are specified after the optional compiler arguments, then an interactive Scala shell is started.  Otherwise, either a script file is run, or a pre-compiled Scala object is run.  It is possible to distinguish the last two cases by using an explicit -object or -script flag, but usually the program can guess correctly.
JAVACMD Specify the java command to be used for running the Scala code. Arguments may be specified as part of the environment variable; spaces, quotation marks, etc., will be passed directly to the shell for expansion.
JAVA_HOME Specify JDK/JRE home directory. This directory is used to locate the java command unless JAVACMD variable set.
JAVA_OPTS Specify the options to be passed to the java command defined by JAVACMD.
With Java 1.5 (or newer) one may for example configure the memory usage of the JVM as follows: JAVA_OPTS="-Xmx512M -Xms16M -Xss16M"
Here are some examples of running Scala code:
Execute a Scala program generated in the current directory scala hello.HelloWorld
Execute a Scala program generated in a user-defined directory classes scala -classpath classes hello.HelloWorld
Execute a Scala program using a user-defined java command env JAVACMD=/usr/local/bin/cacao scala -classpath classes hello.HelloWorld
Execute a Scala program using JVM options env JAVACMD=java JAVA_OPTS="-Dmsg=hello -enableassertions" scala -classpath classes hello.HelloWorld
Here is a complete Scala script for Unix:
#!/bin/sh exec scala "$0" "$@" !# Console.println("Hello, world!") args.toList foreach Console.println
Here is a complete Scala script for MS Windows:
::#! @echo off call scala %0 %* goto :eof ::!# Console.println("Hello, world!") args.toList foreach Console.println
If you want to use the compilation cache to speed up multiple executions of the script, then add -savecompiled to the scala command:
#!/bin/sh exec scala -savecompiled "$0" "$@" !# Console.println("Hello, world!") args.toList foreach Console.println
The scala command returns a zero exit status if it succeeds. Non zero is returned in case of any error.  If a script or top-level object is executed and returns a value, then that return value is passed on to scala.
Written by Martin Odersky and other members of the Scala team.
Report bugs to https://issues.scala-lang.org/.
This is open-source software, available to you under a BSD-like license. See accompanying "copyright" or "LICENSE" file for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
fsc(1), scalac(1), scaladoc(1), scalap(1)
TEST(1P)                    POSIX Programmer's Manual                   TEST(1P)
test — evaluate expression
test [expression]
[ [expression] ]
The test utility shall evaluate the expression and indicate the result of the evaluation by its exit status. An exit status of zero indicates that the expression evaluated as true and an exit status of 1 indicates that the expression evaluated as false.
In the second form of the utility, where the utility name used is [ rather than test, the application shall ensure that the closing square bracket is a separate argument. The test and [ utilities may be implemented as a single linked utility which examines the basename of the zeroth command line argument to determine whether to behave as the test or [ variant. Applications using the exec() family of functions to execute these utilities shall ensure that the argument passed in arg0 or argv[0] is '[' when executing the [ utility and has a basename of "test" when executing the test utility.
The test utility shall not recognize the "--" argument in the manner specified by Guideline 10 in the Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
No options shall be supported.
The application shall ensure that all operators and elements of primaries are presented as separate arguments to the test utility.
The following primaries can be used to construct expression:
-b pathname True if pathname resolves to an existing directory entry for a block special file.  False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a block special file.
-c pathname True if pathname resolves to an existing directory entry for a character special file.  False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a character special file.
-d pathname True if pathname resolves to an existing directory entry for a directory. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a directory.
-e pathname True if pathname resolves to an existing directory entry. False if pathname cannot be resolved.
-f pathname True if pathname resolves to an existing directory entry for a regular file. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a regular file.
-g pathname True if pathname resolves to an existing directory entry for a file that has its set-group-ID flag set. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that does not have its set-group-ID flag set.
-h pathname True if pathname resolves to an existing directory entry for a symbolic link. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a symbolic link. If the final component of pathname is a symbolic link, that symbolic link is not followed.
-L pathname True if pathname resolves to an existing directory entry for a symbolic link. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a symbolic link. If the final component of pathname is a symbolic link, that symbolic link is not followed.
-n string True if the length of string is non-zero; otherwise, false.
-p pathname True if pathname resolves to an existing directory entry for a FIFO. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a FIFO.
-r pathname True if pathname resolves to an existing directory entry for a file for which permission to read from the file will be granted, as defined in Section 1.1.1.4, File Read, Write, and Creation.  False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file for which permission to read from the file will not be granted.
-S pathname True if pathname resolves to an existing directory entry for a socket. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that is not a socket.
-s pathname True if pathname resolves to an existing directory entry for a file that has a size greater than zero. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that does not have a size greater than zero.
-t file_descriptor True if file descriptor number file_descriptor is open and is associated with a terminal. False if file_descriptor is not a valid file descriptor number, or if file descriptor number file_descriptor is not open, or if it is open but is not associated with a terminal.
-u pathname True if pathname resolves to an existing directory entry for a file that has its set-user-ID flag set. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file that does not have its set-user-ID flag set.
-w pathname True if pathname resolves to an existing directory entry for a file for which permission to write to the file will be granted, as defined in Section 1.1.1.4, File Read, Write, and Creation. False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file for which permission to write to the file will not be granted.
-x pathname True if pathname resolves to an existing directory entry for a file for which permission to execute the file (or search it, if it is a directory) will be granted, as defined in Section 1.1.1.4, File Read, Write, and Creation.  False if pathname cannot be resolved, or if pathname resolves to an existing directory entry for a file for which permission to execute (or search) the file will not be granted.
-z string True if the length of string string is zero; otherwise, false.
string    True if the string string is not the null string; otherwise, false.
s1 = s2   True if the strings s1 and s2 are identical; otherwise, false.
s1 != s2  True if the strings s1 and s2 are not identical; otherwise, false.
n1 -eq n2 True if the integers n1 and n2 are algebraically equal; otherwise, false.
n1 -ne n2 True if the integers n1 and n2 are not algebraically equal; otherwise, false.
n1 -gt n2 True if the integer n1 is algebraically greater than the integer n2; otherwise, false.
n1 -ge n2 True if the integer n1 is algebraically greater than or equal to the integer n2; otherwise, false.
n1 -lt n2 True if the integer n1 is algebraically less than the integer n2; otherwise, false.
n1 -le n2 True if the integer n1 is algebraically less than or equal to the integer n2; otherwise, false.
expression1 -a expression2 True if both expression1 and expression2 are true; otherwise, false. The -a binary primary is left associative. It has a higher precedence than -o.
expression1 -o expression2 True if either expression1 or expression2 is true; otherwise, false. The -o binary primary is left associative.
With the exception of the -h pathname and -L pathname primaries, if a pathname argument is a symbolic link, test shall evaluate the expression by resolving the symbolic link and using the file referenced by the link.
These primaries can be combined with the following operators:
! expression True if expression is false. False if expression is true.
( expression ) True if expression is true. False if expression is false. The parentheses can be used to alter the normal precedence and associativity.
The primaries with two elements of the form:
-primary_operator primary_operand
are known as unary primaries.  The primaries with three elements in either of the two forms:
primary_operand -primary_operator primary_operand
primary_operand primary_operator primary_operand
are known as binary primaries.  Additional implementation-defined operators and primary_operators may be provided by implementations. They shall be of the form -operator where the first character of operator is not a digit.
The algorithm for determining the precedence of the operators and the return value that shall be generated is based on the number of arguments presented to test.  (However, when using the "[...]" form, the <right- square-bracket> final argument shall not be counted in this algorithm.)
In the following list, $1, $2, $3, and $4 represent the arguments presented to test:
0 arguments: Exit false (1).
1 argument: Exit true (0) if $1 is not null; otherwise, exit false.
2 arguments: *  If $1 is '!', exit true if $2 is null, false if $2 is not null.
*  If $1 is a unary primary, exit true if the unary test is true, false if the unary test is false.
*  Otherwise, produce unspecified results.
3 arguments: *  If $2 is a binary primary, perform the binary test of $1 and $3.
*  If $1 is '!', negate the two-argument test of $2 and $3.
*  If $1 is '(' and $3 is ')', perform the unary test of $2. On systems that do not support the XSI option, the results are unspecified if $1 is '(' and $3 is ')'.
4 arguments: *  If $1 is '!', negate the three-argument test of $2, $3, and $4.
*  If $1 is '(' and $4 is ')', perform the two-argument test of $2 and $3.  On systems that do not support the XSI option, the results are unspecified if $1 is '(' and $4 is ')'.
*  Otherwise, the results are unspecified.
>4 arguments: The results are unspecified.
On XSI-conformant systems, combinations of primaries and operators shall be evaluated using the precedence and associativity rules described previously. In addition, the string comparison binary primaries '=' and "!=" shall have a higher precedence than any unary primary.
The following environment variables shall affect the execution of test:
0    expression evaluated to true.
1    expression evaluated to false or expression was missing.
>1    An error occurred.
The XSI extensions specifying the -a and -o binary primaries and the '(' and ')' operators have been marked obsolescent. (Many expressions using them are ambiguously defined by the grammar depending on the specific expressions being evaluated.) Scripts using these expressions should be converted to the forms given below. Even though many implementations will continue to support these obsolescent forms, scripts should be extremely careful when dealing with user-supplied input that could be confused with these and other primaries and operators. Unless the application developer knows all the cases that produce input to the script, invocations like:
test "$1" -a "$2"
should be written as:
test "$1" && test "$2"
to avoid problems if a user supplied values such as $1 set to '!'  and $2 set to the null string. That is, in cases where maximal portability is of concern, replace:
test expr1 -a expr2
test expr1 && test expr2
and replace:
test expr1 -o expr2
test expr1 || test expr2
but note that, in test, -a has higher precedence than -o while "&&" and "||" have equal precedence in the shell.
Parentheses or braces can be used in the shell command language to effect grouping.
Parentheses must be escaped when using sh; for example:
test \( expr1 -a expr2 \) -o expr3
This command is not always portable even on XSI-conformant systems depending on the expressions specified by expr1, expr2, and expr3.  The following form can be used instead:
( test expr1 && test expr2 ) || test expr3
The two commands:
test "$1" test ! "$1"
could not be used reliably on some historical systems. Unexpected results would occur if such a string expression were used and $1 expanded to '!', '(', or a known unary primary. Better constructs are:
test -n "$1" test -z "$1"
Historical systems have also been unreliable given the common construct:
test "$response" = "expected string"
One of the following is a more reliable form:
test "X$response" = "Xexpected string" test "expected string" = "$response"
Note that the second form assumes that expected string could not be confused with any unary primary. If expected string starts with '-', '(', '!', or even '=', the first form should be used instead. Using the preceding rules without the XSI marked extensions, any of the three comparison forms is reliable, given any input. (However, note that the strings are quoted in all cases.)
Because the string comparison binary primaries, '=' and "!=", have a higher precedence than any unary primary in the greater than 4 argument case, unexpected results can occur if arguments are not properly prepared. For example, in:
test -d $1 -o -d $2
If $1 evaluates to a possible directory name of '=', the first three arguments are considered a string comparison, which shall cause a syntax error when the second -d is encountered. One of the following forms prevents this; the second is preferred:
test \( -d "$1" \) -o \( -d "$2" \) test -d "$1" || test -d "$2"
Also in the greater than 4 argument case:
test "$1" = "bat" -a "$2" = "ball"
syntax errors occur if $1 evaluates to '(' or '!'.  One of the following forms prevents this; the third is preferred:
test "X$1" = "Xbat" -a "X$2" = "Xball" test "$1" = "bat" && test "$2" = "ball" test "X$1" = "Xbat" && test "X$2" = "Xball"
Note that none of the following examples are permitted by the syntax described:
[-f file] [-f file ] [ -f file] [ -f file test -f file ]
In the first two cases, if a utility named [‐f exists, that utility would be invoked, and not test.  In the remaining cases, the brackets are mismatched, and the behavior is unspecified. However:
test ! ]
does have a defined meaning, and must exit with status 1. Similarly:
test ]
must exit with status 0.
1. Exit if there are not two or three arguments (two variations):
if [ $# -ne 2 ] && [ $# -ne 3 ]; then exit 1; fi if [ $# -lt 2 ] || [ $# -gt 3 ]; then exit 1; fi
2. Perform a mkdir if a directory does not exist:
test ! -d tempdir && mkdir tempdir
3. Wait for a file to become non-readable:
while test -r thefile do sleep 30 done echo '"thefile" is no longer readable'
4. Perform a command if the argument is one of three strings (two variations):
if [ "$1" = "pear" ] || [ "$1" = "grape" ] || [ "$1" = "apple" ] then command fi
case "$1" in pear|grape|apple) command ;; esac
The KornShell-derived conditional command (double bracket [[]]) was removed from the shell command language description in an early proposal. Objections were raised that the real problem is misuse of the test command ([), and putting it into the shell is the wrong way to fix the problem.  Instead, proper documentation and a new shell reserved word (!) are sufficient.
Tests that require multiple test operations can be done at the shell level using individual invocations of the test command and shell logicals, rather than using the error-prone -o flag of test.
XSI-conformant systems support more than four arguments.
XSI-conformant systems support the combining of primaries with the following constructs:
expression1 -a expression2 True if both expression1 and expression2 are true.
expression1 -o expression2 True if at least one of expression1 and expression2 are true.
( expression ) True if expression is true.
In evaluating these more complex combined expressions, the following precedence rules are used:
*  The unary primaries have higher precedence than the algebraic binary primaries.
*  The unary primaries have lower precedence than the string binary primaries.
*  The unary and binary primaries have higher precedence than the unary string primary.
*  The !  operator has higher precedence than the -a operator, and the -a operator has higher precedence than the -o operator.
*  The -a and -o operators are left associative.
*  The parentheses can be used to alter the normal precedence and associativity.
The BSD and System V versions of -f are not the same. The BSD definition was:
-f file   True if file exists and is not a directory.
The SVID version (true if the file exists and is a regular file) was chosen for this volume of POSIX.1‐2017 because its use is consistent with the -b, -c, -d, and -p operands (file exists and is a specific file type).
The -e primary, possessing similar functionality to that provided by the C shell, was added because it provides the only way for a shell script to find out if a file exists without trying to open the file. Since implementations are allowed to add additional file types, a portable script cannot use:
test -b foo -o -c foo -o -d foo -o -f foo -o -p foo
to find out if foo is an existing file. On historical BSD systems, the existence of a file could be determined by:
test -f foo -o -d foo
but there was no easy way to determine that an existing file was a regular file. An early proposal used the KornShell -a primary (with the same meaning), but this was changed to -e because there were concerns about the high probability of humans confusing the -a primary with the -a binary operator.
The following options were not included in this volume of POSIX.1‐2017, although they are provided by some implementations. These operands should not be used by new implementations for other purposes:
-k file   True if file exists and its sticky bit is set.
-C file   True if file is a contiguous file.
-V file   True if file is a version file.
The following option was not included because it was undocumented in most implementations, has been removed from some implementations (including System V), and the functionality is provided by the shell (see Section 2.6.2, Parameter Expansion.
-l string The length of the string string.
The -b, -c, -g, -p, -u, and -x operands are derived from the SVID; historical BSD does not provide them. The -k operand is derived from System V; historical BSD does not provide it.
On historical BSD systems, test -w directory always returned false because test tried to open the directory for writing, which always fails.
Some additional primaries newly invented or from the KornShell appeared in an early proposal as part of the conditional command ([[]]): s1 > s2, s1 < s2, str = pattern, str != pattern, f1 -nt f2, f1 -ot f2, and f1 -ef f2.  They were not carried forward into the test utility when the conditional command was removed from the shell because they have not been included in the test utility built into historical implementations of the sh utility.
The -t file_descriptor primary is shown with a mandatory argument because the grammar is ambiguous if it can be omitted. Historical implementations have allowed it to be omitted, providing a default of 1.
It is noted that '[' is not part of the portable filename character set; however, since it is required to be encoded by a single byte, and is part of the portable character set, the name of this utility forms a character string across all supported locales.
Section 1.1.1.4, File Read, Write, and Creation, find
MOSQUITTO_PASSWD(1)                 Commands                 MOSQUITTO_PASSWD(1)
mosquitto_passwd - manage password files for mosquitto
mosquitto_passwd [-H hash] [-c | -D] passwordfile username
mosquitto_passwd [-H hash] -b passwordfile username password
mosquitto_passwd -U passwordfile
mosquitto_passwd is a tool for managing password files for the mosquitto MQTT broker.
Usernames must not contain ":". Passwords are stored in a similar format to crypt(3).
-b Run in batch mode. This allows the password to be provided at the command line which can be convenient but should be used with care because the password will be visible on the command line and in command history.
-c Create a new password file. If the file already exists, it will be overwritten.
-D Delete the specified user from the password file.
-H Choose the hash to use. Can be one of sha512-pbkdf2 or sha512. Defaults to sha512-pbkdf2. The sha512 option is provided for creating password files for use with Mosquitto 1.6 and earlier.
-U This option can be used to upgrade/convert a password file with plain text passwords into one using hashed passwords. It will modify the specified file. It does not detect whether passwords are already hashed, so using it on a password file that already contains hashed passwords will generate new hashes based on the old hashes and render the password file unusable.
passwordfile The password file to modify.
username The username to add/update/delete.
password The password to use when in batch mode.
mosquitto_sub returns zero on success, or non-zero on error. If the connection is refused by the broker at the MQTT level, then the exit code is the CONNACK reason code. If another error occurs, the exit code is a libmosquitto return value.
MQTT v3.1.1 CONNACK codes:
•   0 Success
•   1 Connection refused: Bad protocol version
•   2 Connection refused: Identifier rejected
•   3 Connection refused: Server unavailable
•   4 Connection refused: Bad username/password
•   5 Connection refused: Not authorized
MQTT v5 CONNACK codes:
•   128 Unspecified error
•   129 Malformed packet
•   130 Protocol error
•   131 Implementation specific error
•   132 Unsupported protocol version
•   133 Client ID not valid
•   134 Bad username or password
•   135 Not authorized
•   136 Server unavailable
•   137 Server busy
•   138 Banned
•   139 Server shutting down
•   140 Bad authentication method
•   141 Keep alive timeout
•   142 Session taken over
•   143 Topic filter invalid
•   144 Topic name invalid
•   147 Receive maximum exceeded
•   148 Topic alias invalid
•   149 Packet too large
•   148 Message rate too high
•   151 Quota exceeded
•   152 Administrative action
•   153 Payload format invalid
•   154 Retain not supported
•   155 QoS not supported
•   156 Use another server
•   157 Server moved
•   158 Shared subscriptions not supported
•   159 Connection rate exceeded
•   160 Maximum connect time
•   161 Subscription IDs not supported
•   162 Wildcard subscriptions not supported
Add a user to a new password file:
•   mosquitto_passwd -c /etc/mosquitto/passwd ral
Delete a user from a password file
•   mosquitto_passwd -D /etc/mosquitto/passwd ral
mosquitto(8), mosquitto.conf(5), mqtt(7)
i7z(1)                       General Commands Manual                      i7z(1)
i7z - A better i7 (and now i3, i5) reporting tool for Linux.
i7z [OPTION], [OPTION] is optional. i7z needs to be run in super user (root) mode.
i7z runs the i7z, ncurses based, program without any options. i7z will print out the C-states and temperature for i3, i5 and i7 based Core processors from Intel (including Nehalems, Sandy Bridge and Ivy Bridge).
-h, --help show the list of options available with the i7z tool.
-w  [a|l],  --write  [a,l] Logging of the frequencies can be turned on with this options. Option "-w a" or "--write a" will append to the  log file. Option "-w l" or "--write l" will replace the log file.
-l,  --logfile  [FILENAME] Change  the  log file name to the specified FILENAME. Default logging file is cpu_freq_log.txt (single  socket) or cpu_freq_log_dual%d.txt (dual socket, %d is either 0, 1).
--socket0  [SOCKETNUM], --socket1 [SOCKETNUM] The tool can print information for about 2 sockets at once at the most. The top view  will be, by  default, of the first socket (controlled by --socket0) and the bottom view will be of the second socket (controlled by --socket1). Supply the appropriate value of 0 or 1 or more for SOCKETNUM (if there are more sockets on the machine) to show in the top and bottom view.
--nogui Disable the GUI. Useful when the only need is logging.
Example To print for two sockets and also change the log file (log to /tmp/logfilei7z)
i7z --socket0 0 --socket1 1 -logfile /tmp/logfilei7z -w l
Do report bugs or feature enhancement as an issue at http://code.google.com/p/i7z.
Written in 2010, by Abhishek Jaiantilal (abhirana @ gmail.com). i7z  is licensed  under the terms of the GNU  General Public License (GPL) version 2.
JUPYTER(1)                        User Commands                       JUPYTER(1)
jupyter - obtain user-related paths for Jupyter
jupyter [-h] [--version] [--config-dir] [--data-dir] [--runtime-dir] [--paths] [--json] [subcommand]
positional arguments: subcommand the subcommand to launch
--version show the jupyter command's version and exit
--config-dir show Jupyter config dir
--data-dir show Jupyter data dir
--runtime-dir show Jupyter runtime dir
--paths show all Jupyter paths. Add --json for machine-readable format.
--json output paths as machine-readable json
Available subcommands: migrate troubleshoot
A2ENSITE(8)                  System Manager's Manual                 A2ENSITE(8)
a2ensite, a2dissite - enable or disable an apache2 site / virtual host
a2ensite [-q|--quiet] [-m|--maintmode] [ site ]
a2dissite [-q|--quiet] [-m|--maintmode] [-p|--purge] [ site ]
This manual page documents briefly the a2ensite and a2dissite commands.
a2ensite is a script that enables the specified site (which contains a <VirtualHost> block) within the apache2 configuration.  It does this by creating symlinks within /etc/apache2/sites-enabled.  Likewise, a2dissite disables a site by removing those symlinks.  It is not an error to enable a site which is already enabled, or to disable one which is already disabled.
Apache treats the very first virtual host enabled specially as every request not matching any actual directive is being redirected there. Thus it should be called 000-default in order to sort before the remaining hosts to be loaded first.
a2ensite and a2dissite exit with status 0 if all sites are processed successfully, 1 if errors occur, 2 if an invalid option was used.
a2dissite 000-default
Disables the default site.
/etc/apache2/sites-available Directory with files giving information on available sites.
/etc/apache2/sites-enabled Directory with links to the files in sites-available for enabled sites.
apache2ctl(8), a2enmod(8), a2dismod(8), a2enconf(8), a2disconf(8).
This manual page was written by Stefan Fritsch <sf@debian.org> (based on the a2enmod manual page by Daniel Stone <daniel@sfarc.net>) for the Debian GNU/Linux distribution.
gh-ssh-key - Manage SSH keys
gh ssh-key <command> [flags]
Manage SSH keys registered with your GitHub account
gh(1), gh-ssh-key-add(1), gh-ssh-key-list(1)
VNSTATI(1)                        User Manuals                        VNSTATI(1)
vnstati - png image output support for vnStat
vnstati [-5bcdDehiLmosStvy?]  [-5g [limit] [height]] [--altdate] [--begin date] [--cache time] [--config file] [--days [limit]] [--dbdir directory] [--debug] [--end date] [--fivegraph [limit] [height]] [--fiveminutes [limit]] [--headertext text] [--help] [-hg] [--hours [limit]] [--hoursgraph] [-hs [graph]] [--hsummary [graph]] [-i interface] [--iface interface] [--large] [--limit limit] [--locale locale] [--months [limit]] [-ne] [-nh] [-nl] [--noedge] [--noheader] [--nolegend] [--output file] [-ru [mode]] [--rateunit [mode]] [--scale percent] [--small] [--style number] [--summary] [--top [limit]] [--transparent [enabled]] [--version] [-vs [graph]] [--vsummary [graph]] [--months [limit]] [interface]
The purpose of vnstati is to provide image output support for statistics collected using vnstat(1).  The image file format is limited to png. All basic outputs of vnStat are supported excluding live traffic features. The image can be outputted either to a file or to standard output.
--altdate Use alternative date and time text location. The date and time text will be moved from the upper right header section to the lower left corner. This option will have no effect if -nh, --noheader has been selected.
-b, --begin date Begin the list output with a specific date / time defined by date instead of the begin being selected based on the number of entries to be shown.  If date isn't available in the database then the closest later date will be used.  date supports the following formats: YYYY-MM-DD HH:MM and YYYY-MM-DD.  This option can only be used with list outputs.
-c, --cache time Update output file only if at least time minutes have passed since the previous file update. This option is ignored if stdout is used as output.
--config file Use file as configuration file instead of using automatic configuration file search functionality.
-d, --days [limit] Output traffic statistics on a daily basis for the last days. The length of the list will be limited to 30 entries unless configured otherwise or unless the optional limit parameter is used. All entries stored in the database will be shown if limit is set to 0.
--dbdir directory Use directory as database directory instead of using the directory specified in the configuration file or the hardcoded default if no configuration file is available.
-D, --debug Show additional debug output.
-e, --end date End the list output with a specific date / time defined by date instead of the latest date / time in the database. If date isn't available in the database then the closest earlier date will be used.  date supports the following formats: YYYY-MM-DD HH:MM and YYYY-MM-DD.  This option can only be used with list outputs. The top list also requires --begin to be used at the same time with this option.
-5g, --fivegraph [limit] [height] Output traffic statistics with a 5 minute resolution for the last 48 hours using a bar graph. The width of the graph can be modified using the optional limit parameter which represents the number of 5 minute entries with 12 entries for each hour. The smallest supported value is 288 (last 24 hours). Additionally, the height of the graph can be modified using the optional height parameter. The smallest supported height is 150 pixels.
-5, --fiveminutes [limit] Output traffic statistics with a 5 minute resolution for the last hours.  The length of the list will be limited to 24 entries unless configured otherwise or unless the optional limit parameter is used. All entries stored in the database will be shown if limit is set to 0.
--headertext text Show text in image header section instead of automatically generated interface identification.  text is limited to 64 characters and may not get completely shown if longer than the width of the image. Use with --altdate if maximal space is needed. This option will have no effect if -nh, --noheader has been selected.
-h, --hours [limit] Output traffic statistics on a hourly basis. The length of the list will be limited to 24 entries unless configured otherwise or unless the optional limit parameter is used. All entries store in the database will be shown if the limit is set to 0.
-hg, --hoursgraph Output traffic statistics on a hourly basis for the last 24 hours using a bar graph.
-hs, --hsummary [graph] Output traffic summary with the graph selected using the SummaryGraph setting in the configuration file next to it using a horizontal layout. The optional graph parameter can be used to override the configuration file setting. Available graphs: 0 = hours, 1 = 5 minutes.
-i, --iface interface Use interface instead of default or configured interface. It is also possible to merge the information of two or more interfaces using the interface1+interface2+...  syntax.  All provided interfaces must be unique and must exist in the database when the merge syntax is used.
-L, --large Use large fonts in output.
--limit limit Set the maximum number of shown entries in list outputs to limit. Usage of --limit overrides the default list entry limit values and the optional limit parameter given directly for a list query. All entries stored in the database will be shown if limit is set to 0.
--locale locale Use locale instead of using the locale setting specified in the configuration file or the system default if no configuration file is available.
-m, --months [limit] Output traffic statistics on a monthly basis for the last months. The length of the list will be limited to 12 entries unless configured otherwise or unless the optional limit parameter is used. All entries stored in the database will be shown if limit is set to 0.
-ne, --noedge Remove darker edges from around the image.
-nh, --noheader Remove header containing title and update time. Time of the previous update will still be visible in the lower right corner using a less visible color.
-nl, --nolegend Remove legend containing rx and tx color mapping information from the image.
-o, --output file Write png image to file and exit. Output can be directed to stdout by giving "-" as filename.
-ru, --rateunit [mode] Swap the configured rate unit. If rate has been configured to be shown in bytes then rate will be shown in bits if this option is present. In the same way, if rate has been configured to be shown in bits then rate will be shown in bytes when this option is present. Alternatively, mode with either 0 or 1 can be used as parameter for this option in order to select between bytes (0) and bits (1) regardless of the configuration file setting.
--scale percent Scale output to given percent resulting in the image being either smaller or larger than the default size.
-S, --small Use small fonts in output.
--style number Modify the content and style of outputs. Setting number to 3 will show average traffic rate in all outputs where it is supported. Other values will show bar graphics instead.
-s, --summary Output traffic statistics summary.
-t, --top [limit] Output all time top traffic days. The length of the list will be limited to 10 entries unless configured otherwise or unless the optional limit parameter is used. All entries stored in the database will be shown if limit is set to 0. When used with --begin and optionally with --end, the list will be generated using the daily data instead of separate top entries.  The availability of daily data defines the boundaries the date specific query can access.
--transparent [enabled] Toggle background color transparency depending of the TransparentBg setting in the configuration file. Alternatively, 0 or 1 can be given as parameter enabled for this option in order to either disable (0) or enable (1) transparency regardless of the configuration file setting.
-v, --version Show current version.
-vs, --vsummary [graph] Output traffic summary with the graph selected using the SummaryGraph setting in the configuration file below it using a vertical layout. The optional graph parameter can be used to override the configuration file setting. Available graphs: 0 = hours, 1 = 5 minutes.
-y, --years [limit] Output traffic statistics on a yearly basis for the last years. The list will show all entries by default unless configured otherwise or unless the optional limit parameter is used. All entries stored in the database will also be shown if limit is set to 0.
-?, --help Show a command option summary.
/var/lib/vnstat/ Default database directory.
/etc/vnstat.conf Config file that will be used unless $HOME/.vnstatrc exists. See vnstat.conf(5) for more information.
vnstati -s -i eth0 -o /tmp/vnstat.png Output traffic summary for interface eth0 to file /tmp/vnstat.png.
vnstati -vs -i eth0+eth1+eth2 -o /tmp/vnstat.png Output traffic summary with hourly data under the normal summary for a merge of interfaces eth0, eth1 and eth2 to file /tmp/vnstat.png.
vnstati -h -c 15 -o /tmp/vnstat_h.png Output hourly traffic statistics for default interface to file /tmp/vnstat_h.png if the file has not been updated within the last 15 minutes.
vnstati -d -ne -nh -o - Output daily traffic statistics without displaying the header section and edges for default interface to standard output (stdout).
vnstati -m --config /home/me/vnstat.cfg -i -o - Output monthly traffic statistics for default interface specified in configuration file /home/me/vnstat.cfg to standard output (stdout).
Depending on the built-in fonts provided by the GD library, not all characters may end up shown correctly when a UTF-8 locale is used.