neulab/tldr huggingface dataset:
unicode: All printable Unicode characters are considered when determining if a list of integers is to be displayed in string syntax. This can give unexpected results if, for example, your font does not cover all Unicode characters.
See also io:printable_range/0 in STDLIB.
+P Number: Sets the maximum number of simultaneously existing processes for this system if a Number is passed as value. Valid range for Number is [1024-134217727]
NOTE: The actual maximum chosen may be much larger than the Number passed. Currently the runtime system often, but not always, chooses a value that is a power of 2. This might, however, be changed in the future. The actual value chosen can be checked by calling erlang:system_info(process_limit).
The default value is 262144
+Q Number: Sets the maximum number of simultaneously existing ports for this system if a Number is passed as value. Valid range for Number is [1024-134217727]
NOTE: The actual maximum chosen may be much larger than the actual Number passed. Currently the runtime system often, but not always, chooses a value that is a power of 2. This might, however, be changed in the future. The actual value chosen can be checked by calling erlang:system_info(port_limit).
The default value used is normally 65536. However, if the runtime system is able to determine maximum amount of file descriptors that it is allowed to open and this value is larger than 65536, the chosen value will increased to a value larger or equal to the maximum amount of file descriptors that can be opened.
On Windows the default value is set to 8196 because the normal OS limitations are set higher than most machines can handle.
+R ReleaseNumber: Sets the compatibility mode.
The distribution mechanism is not backward compatible by default. This flag sets the emulator in compatibility mode with an earlier Erlang/OTP release ReleaseNumber. The release number must be in the range <current release>-2..<current release>. This limits the emulator, making it possible for it to communicate with Erlang nodes (as well as C- and Java nodes) running that earlier release.
Note: Ensure that all nodes (Erlang-, C-, and Java nodes) of a distributed Erlang system is of the same Erlang/OTP release, or from two different Erlang/OTP releases X and Y, where all Y nodes have compatibility mode X.
+r: Forces ETS memory block to be moved on realloc.
+rg ReaderGroupsLimit: Limits the number of reader groups used by read/write locks optimized for read operations in the Erlang runtime system. By default the reader groups limit is 64.
When the number of schedulers is less than or equal to the reader groups limit, each scheduler has its own reader group. When the number of schedulers is larger than the reader groups limit, schedulers share reader groups. Shared reader groups degrade read lock and read unlock performance while many reader groups degrade write lock performance. So, the limit is a tradeoff between performance for read operations and performance for write operations. Each reader group consumes 64 byte in each read/write lock.
Notice that a runtime system using shared reader groups benefits from binding schedulers to logical processors, as the reader groups are distributed better between schedulers.
+S Schedulers:SchedulerOnline: Sets the number of scheduler threads to create and scheduler threads to set online. The maximum for both values is 1024. If the Erlang runtime system is able to determine the number of logical processors configured and logical processors available, Schedulers defaults to logical processors configured, and SchedulersOnline defaults to logical processors available; otherwise the default values are 1. If the emulator detects that it is subject to a CPU quota, the default value for SchedulersOnline will be limited accordingly.
Schedulers can be omitted if :SchedulerOnline is not and conversely. The number of schedulers online can be changed at runtime through erlang:system_flag(schedulers_online, SchedulersOnline).
If Schedulers or SchedulersOnline is specified as a negative number, the value is subtracted from the default number of logical processors configured or logical processors available, respectively.
Specifying value 0 for Schedulers or SchedulersOnline resets the number of scheduler threads or scheduler threads online, respectively, to its default value.
+SP SchedulersPercentage:SchedulersOnlinePercentage: Similar to +S but uses percentages to set the number of scheduler threads to create, based on logical processors configured, and scheduler threads to set online, based on logical processors available. Specified values must be > 0. For example, +SP 50:25 sets the number of scheduler threads to 50% of the logical processors configured, and the number of scheduler threads online to 25% of the logical processors available. SchedulersPercentage can be omitted if :SchedulersOnlinePercentage is not and conversely. The number of schedulers online can be changed at runtime through erlang:system_flag(schedulers_online, SchedulersOnline).
This option interacts with +S settings. For example, on a system with 8 logical cores configured and 8 logical cores available, the combination of the options +S 4:4 +SP 50:25 (in either order) results in 2 scheduler threads (50% of 4) and 1 scheduler thread online (25% of 4).
+SDcpu DirtyCPUSchedulers:DirtyCPUSchedulersOnline: Sets the number of dirty CPU scheduler threads to create and dirty CPU scheduler threads to set online. The maximum for both values is 1024, and each value is further limited by the settings for normal schedulers:
* The number of dirty CPU scheduler threads created cannot exceed the number of normal scheduler threads created.
* The number of dirty CPU scheduler threads online cannot exceed the number of normal scheduler threads online.
For details, see the +S and +SP. By default, the number of dirty CPU scheduler threads created equals the number of normal scheduler threads created, and the number of dirty CPU scheduler threads online equals the number of normal scheduler threads online. DirtyCPUSchedulers can be omitted if :DirtyCPUSchedulersOnline is not and conversely. The number of dirty CPU schedulers online can be changed at runtime through erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).
The amount of dirty CPU schedulers is limited by the amount of normal schedulers in order to limit the effect on processes executing on ordinary schedulers. If the amount of dirty CPU schedulers was allowed to be unlimited, dirty CPU bound jobs would potentially starve normal jobs.
Typical users of the dirty CPU schedulers are large garbage collections, json protocol encode/decoders written as nifs and matrix manipulation libraries.
You can use msacc(3erl) in order to see the current load of the dirty CPU schedulers threads and adjust the number used accordingly.
+SDPcpu DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercentage: Similar to +SDcpu but uses percentages to set the number of dirty CPU scheduler threads to create and the number of dirty CPU scheduler threads to set online. Specified values must be > 0. For example, +SDPcpu 50:25 sets the number of dirty CPU scheduler threads to 50% of the logical processors configured and the number of dirty CPU scheduler threads online to 25% of the logical processors available. DirtyCPUSchedulersPercentage can be omitted if :DirtyCPUSchedulersOnlinePercentage is not and conversely. The number of dirty CPU schedulers online can be changed at runtime through erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).
This option interacts with +SDcpu settings. For example, on a system with 8 logical cores configured and 8 logical cores available, the combination of the options +SDcpu 4:4 +SDPcpu 50:25 (in either order) results in 2 dirty CPU scheduler threads (50% of 4) and 1 dirty CPU scheduler thread online (25% of 4).
+SDio DirtyIOSchedulers: Sets the number of dirty I/O scheduler threads to create. Valid range is 1-1024. By default, the number of dirty I/O scheduler threads created is 10.
The amount of dirty IO schedulers is not limited by the amount of normal schedulers like the amount of dirty CPU schedulers. This since only I/O bound work is expected to execute on dirty I/O schedulers. If the user should schedule CPU bound jobs on dirty I/O schedulers, these jobs might starve ordinary jobs executing on ordinary schedulers.
Typical users of the dirty IO schedulers are reading and writing to files.
You can use msacc(3erl) in order to see the current load of the dirty IO schedulers threads and adjust the number used accordingly.
+sFlag Value: Scheduling specific flags.
+sbt BindType: Sets scheduler bind type.
Schedulers can also be bound using flag +stbt. The only difference between these two flags is how the following errors are handled:
* Binding of schedulers is not supported on the specific platform.
* No available CPU topology. That is, the runtime system was not able to detect the CPU topology automatically, and no user- defined CPU topology was set.
If any of these errors occur when +sbt has been passed, the runtime system prints an error message, and refuses to start. If any of these errors occur when +stbt has been passed, the runtime system silently ignores the error, and start up using unbound schedulers.
Valid BindTypes:
u: unbound - Schedulers are not bound to logical processors, that is, the operating system decides where the scheduler threads execute, and when to migrate them. This is the default.
ns: no_spread - Schedulers with close scheduler identifiers are bound as close as possible in hardware.
ts: thread_spread - Thread refers to hardware threads (such as Intel's hyper-threads). Schedulers with low scheduler identifiers, are bound to the first hardware thread of each core, then schedulers with higher scheduler identifiers are bound to the second hardware thread of each core,and so on.
ps: processor_spread - Schedulers are spread like thread_spread, but also over physical processor chips.
s: spread - Schedulers are spread as much as possible.
nnts: no_node_thread_spread - Like thread_spread, but if multiple Non- Uniform Memory Access (NUMA) nodes exist, schedulers are spread over one NUMA node at a time, that is, all logical processors of one NUMA node are bound to schedulers in sequence.
nnps: no_node_processor_spread - Like processor_spread, but if multiple NUMA nodes exist, schedulers are spread over one NUMA node at a time, that is, all logical processors of one NUMA node are bound to schedulers in sequence.
tnnps: thread_no_node_processor_spread - A combination of thread_spread, and no_node_processor_spread. Schedulers are spread over hardware threads across NUMA nodes, but schedulers are only spread over processors internally in one NUMA node at a time.
db: default_bind - Binds schedulers the default way. Defaults to thread_no_node_processor_spread (which can change in the future).
Binding of schedulers is only supported on newer Linux, Solaris, FreeBSD, and Windows systems.
If no CPU topology is available when flag +sbt is processed and BindType is any other type than u, the runtime system fails to start. CPU topology can be defined using flag +sct. Notice that flag +sct can have to be passed before flag +sbt on the command line (if no CPU topology has been automatically detected).
The runtime system does by default not bind schedulers to logical processors.
Note: If the Erlang runtime system is the only operating system process that binds threads to logical processors, this improves the performance of the runtime system. However, if other operating system processes (for example another Erlang runtime system) also bind threads to logical processors, there can be a performance penalty instead. This performance penalty can sometimes be severe. If so, you are advised not to bind the schedulers.
How schedulers are bound matters. For example, in situations when there are fewer running processes than schedulers online, the runtime system tries to migrate processes to schedulers with low scheduler identifiers. The more the schedulers are spread over the hardware, the more resources are available to the runtime system in such situations.
Note: If a scheduler fails to bind, this is often silently ignored, as it is not always possible to verify valid logical processor identifiers. If an error is reported, it is reported to the error_logger. If you want to verify that the schedulers have bound as requested, call erlang:system_info(scheduler_bindings).
+sbwt none|very_short|short|medium|long|very_long: Sets scheduler busy wait threshold. Defaults to medium. The threshold determines how long schedulers are to busy wait when running out of work before going to sleep.
Note: This flag can be removed or changed at any time without prior notice.
+sbwtdcpu none|very_short|short|medium|long|very_long: As +sbwt but affects dirty CPU schedulers. Defaults to short.
+sbwtdio none|very_short|short|medium|long|very_long: As +sbwt but affects dirty IO schedulers. Defaults to short.
+scl true|false: Enables or disables scheduler compaction of load. By default scheduler compaction of load is enabled. When enabled, load balancing strives for a load distribution, which causes as many scheduler threads as possible to be fully loaded (that is, not run out of work). This is accomplished by migrating load (for example, runnable processes) into a smaller set of schedulers when schedulers frequently run out of work. When disabled, the frequency with which schedulers run out of work is not taken into account by the load balancing logic.
+scl false is similar to +sub true, but +sub true also balances scheduler utilization between schedulers.
+sct CpuTopology:
* <Id> = integer(); when 0 =< <Id> =< 65535
* <IdRange> = <Id>-<Id>
* <IdOrIdRange> = <Id> | <IdRange>
* <IdList> = <IdOrIdRange>,<IdOrIdRange> | <IdOrIdRange>
* <LogicalIds> = L<IdList>
* <ThreadIds> = T<IdList> | t<IdList>
* <CoreIds> = C<IdList> | c<IdList>
* <ProcessorIds> = P<IdList> | p<IdList>
* <NodeIds> = N<IdList> | n<IdList>
* <IdDefs> = <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds> | <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>
* CpuTopology = <IdDefs>:<IdDefs> | <IdDefs>
Sets a user-defined CPU topology. The user-defined CPU topology overrides any automatically detected CPU topology. The CPU topology is used when binding schedulers to logical processors.
Uppercase letters signify real identifiers and lowercase letters signify fake identifiers only used for description of the topology. Identifiers passed as real identifiers can be used by the runtime system when trying to access specific hardware; if they are incorrect the behavior is undefined. Faked logical CPU identifiers are not accepted, as there is no point in defining the CPU topology without real logical CPU identifiers. Thread, core, processor, and node identifiers can be omitted. If omitted, the thread ID defaults to t0, the core ID defaults to c0, the processor ID defaults to p0, and the node ID is left undefined. Either each logical processor must belong to only one NUMA node, or no logical processors must belong to any NUMA nodes.
Both increasing and decreasing <IdRange>s are allowed.
NUMA node identifiers are system wide. That is, each NUMA node on the system must have a unique identifier. Processor identifiers are also system wide. Core identifiers are processor wide. Thread identifiers are core wide.
The order of the identifier types implies the hierarchy of the CPU topology. The valid orders are as follows:
* <LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>, that is, thread is part of a core that is part of a processor, which is part of a NUMA node.
* <LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>, that is, thread is part of a core that is part of a NUMA node, which is part of a processor.
A CPU topology can consist of both processor external, and processor internal NUMA nodes as long as each logical processor belongs to only one NUMA node. If <ProcessorIds> is omitted, its default position is before <NodeIds>. That is, the default is processor external NUMA nodes.
If a list of identifiers is used in an <IdDefs>:
* <LogicalIds> must be a list of identifiers.
* At least one other identifier type besides <LogicalIds> must also have a list of identifiers.
* All lists of identifiers must produce the same number of identifiers.
A simple example. A single quad core processor can be described as follows:
% erl +sct L0-3c0-3 1> erlang:system_info(cpu_topology). [{processor,[{core,{logical,0}}, {core,{logical,1}}, {core,{logical,2}}, {core,{logical,3}}]}]
A more complicated example with two quad core processors, each processor in its own NUMA node. The ordering of logical processors is a bit weird. This to give a better example of identifier lists:
% erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1 1> erlang:system_info(cpu_topology). [{node,[{processor,[{core,{logical,0}}, {core,{logical,1}}, {core,{logical,3}}, {core,{logical,2}}]}]}, {node,[{processor,[{core,{logical,7}}, {core,{logical,4}}, {core,{logical,6}}, {core,{logical,5}}]}]}]
As long as real identifiers are correct, it is OK to pass a CPU topology that is not a correct description of the CPU topology. When used with care this can be very useful. This to trick the emulator to bind its schedulers as you want. For example, if you want to run multiple Erlang runtime systems on the same machine, you want to reduce the number of schedulers used and manipulate the CPU topology so that they bind to different logical CPUs. An example, with two Erlang runtime systems on a quad core machine:
% erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one % erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two
In this example, each runtime system have two schedulers each online, and all schedulers online will run on different cores. If we change to one scheduler online on one runtime system, and three schedulers online on the other, all schedulers online will still run on different cores.
Notice that a faked CPU topology that does not reflect how the real CPU topology looks like is likely to decrease the performance of the runtime system.
For more information, see erlang:system_info(cpu_topology).
+sfwi Interval: Sets scheduler-forced wakeup interval. All run queues are scanned each Interval milliseconds. While there are sleeping schedulers in the system, one scheduler is woken for each non-empty run queue found. Interval default to 0, meaning this feature is disabled.
Note: This feature has been introduced as a temporary workaround for long- executing native code, and native code that does not bump reductions properly in OTP. When these bugs have been fixed, this flag will be removed.
+spp Bool: Sets default scheduler hint for port parallelism. If set to true, the virtual machine schedules port tasks when it improves parallelism in the system. If set to false, the virtual machine tries to perform port tasks immediately, improving latency at the expense of parallelism. Default to false. The default used can be inspected in runtime by calling erlang:system_info(port_parallelism). The default can be overridden on port creation by passing option parallelism to erlang:open_port/2.
+sss size: Suggested stack size, in kilowords, for scheduler threads. Valid range is 20-8192 kilowords. The default suggested stack size is 128 kilowords.
+sssdcpu size: Suggested stack size, in kilowords, for dirty CPU scheduler threads. Valid range is 20-8192 kilowords. The default suggested stack size is 40 kilowords.
+sssdio size: Suggested stack size, in kilowords, for dirty IO scheduler threads. Valid range is 20-8192 kilowords. The default suggested stack size is 40 kilowords.
+stbt BindType: Tries to set the scheduler bind type. The same as flag +sbt except how some errors are handled. For more information, see +sbt.
+sub true|false: Enables or disables  scheduler utilization balancing of load. By default scheduler utilization balancing is disabled and instead scheduler compaction of load is enabled, which strives for a load distribution that causes as many scheduler threads as possible to be fully loaded (that is, not run out of work). When scheduler utilization balancing is enabled, the system instead tries to balance scheduler utilization between schedulers. That is, strive for equal scheduler utilization on all schedulers.
+sub true is only supported on systems where the runtime system detects and uses a monotonically increasing high-resolution clock. On other systems, the runtime system fails to start.
+sub true implies +scl false. The difference between +sub true and +scl false is that +scl false does not try to balance the scheduler utilization.
+swct very_eager|eager|medium|lazy|very_lazy: Sets scheduler wake cleanup threshold. Defaults to medium. Controls how eager schedulers are to be requesting wakeup because of certain cleanup operations. When a lazy setting is used, more outstanding cleanup operations can be left undone while a scheduler is idling. When an eager setting is used, schedulers are more frequently woken, potentially increasing CPU-utilization.
+sws default|legacy: Sets scheduler wakeup strategy. Default strategy changed in ERTS 5.10 (Erlang/OTP R16A). This strategy was known as proposal in Erlang/OTP R15. The legacy strategy was used as default from R13 up to and including R15.
+swt very_low|low|medium|high|very_high: Sets scheduler wakeup threshold. Defaults to medium. The threshold determines when to wake up sleeping schedulers when more work than can be handled by currently awake schedulers exists. A low threshold causes earlier wakeups, and a high threshold causes later wakeups. Early wakeups distribute work over multiple schedulers faster, but work does more easily bounce between schedulers.
+swtdcpu very_low|low|medium|high|very_high: As +swt but affects dirty CPU schedulers. Defaults to medium.
+swtdio very_low|low|medium|high|very_high: As +swt but affects dirty IO schedulers. Defaults to medium.
+t size: Sets the maximum number of atoms the virtual machine can handle. Defaults to 1,048,576.
+T Level: Enables modified timing and sets the modified timing level. Valid range is 0-9. The timing of the runtime system is changed. A high level usually means a greater change than a low level. Changing the timing can be very useful for finding timing-related bugs.
Modified timing affects the following:
Process spawning: A process calling spawn, spawn_link, spawn_monitor, or spawn_opt is scheduled out immediately after completing the call. When higher modified timing levels are used, the caller also sleeps for a while after it is scheduled out.
Context reductions: The number of reductions a process is allowed to use before it is scheduled out is increased or reduced.
Input reductions: The number of reductions performed before checking I/O is increased or reduced.
Note: Performance suffers when modified timing is enabled. This flag is only intended for testing and debugging.
return_to and return_from trace messages are lost when tracing on the spawn BIFs.
This flag can be removed or changed at any time without prior notice.
+v: Verbose.
+V: Makes the emulator print its version number.
+W w | i | e: Sets the mapping of warning messages for error_logger. Messages sent to the error logger using one of the warning routines can be mapped to errors (+W e), warnings (+W w), or information reports (+W i). Defaults to warnings. The current mapping can be retrieved using error_logger:warning_map/0. For more information, see error_logger:warning_map/0 in Kernel.
+zFlag Value: Miscellaneous flags:
+zdbbl size: Sets the distribution buffer busy limit (dist_buf_busy_limit) in kilobytes. Valid range is 1-2097151. Defaults to 1024.
A larger buffer limit allows processes to buffer more outgoing messages over the distribution. When the buffer limit has been reached, sending processes will be suspended until the buffer size has shrunk. The buffer limit is per distribution channel. A higher limit gives lower latency and higher throughput at the expense of higher memory use.
+zdntgc time: Sets the delayed node table garbage collection time (delayed_node_table_gc) in seconds. Valid values are either infinity or an integer in the range 0-100000000. Defaults to 60.
Node table entries that are not referred linger in the table for at least the amount of time that this parameter determines. The lingering prevents repeated deletions and insertions in the tables from occurring.
ERL_CRASH_DUMP: If the emulator needs to write a crash dump, the value of this variable is the filename of the crash dump file. If the variable is not set, the name of the crash dump file is erl_crash.dump in the current directory.
ERL_CRASH_DUMP_NICE: Unix systems: If the emulator needs to write a crash dump, it uses the value of this variable to set the nice value for the process, thus lowering its priority. Valid range is 1-39 (higher values are replaced with 39). The highest value, 39, gives the process the lowest priority.
ERL_CRASH_DUMP_SECONDS: Unix systems: This variable gives the number of seconds that the emulator is allowed to spend writing a crash dump. When the given number of seconds have elapsed, the emulator is terminated.
ERL_CRASH_DUMP_SECONDS=0: If the variable is set to 0 seconds, the runtime system does not even attempt to write the crash dump file. It only terminates. This is the default if option -heart is passed to erl and ERL_CRASH_DUMP_SECONDS is not set.
ERL_CRASH_DUMP_SECONDS=S: If the variable is set to a positive value S, wait for S seconds to complete the crash dump file and then terminates the runtime system with a SIGALRM signal.
ERL_CRASH_DUMP_SECONDS=-1: A negative value causes the termination of the runtime system to wait indefinitely until the crash dump file has been completly written. This is the default if option -heart is not passed to erl and ERL_CRASH_DUMP_SECONDS is not set.
See also heart(3erl).
ERL_CRASH_DUMP_BYTES: This variable sets the maximum size of a crash dump file in bytes. The crash dump will be truncated if this limit is exceeded. If the variable is not set, no size limit is enforced by default. If the variable is set to 0, the runtime system does not even attempt to write a crash dump file.
Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).
ERL_AFLAGS: The content of this variable is added to the beginning of the command line for erl.
Flag -extra is treated in a special way. Its scope ends at the end of the environment variable content. Arguments following an -extra flag are moved on the command line into section -extra, that is, the end of the command line following an -extra flag.
ERL_ZFLAGS and ERL_FLAGS: The content of these variables are added to the end of the command line for erl.
ERL_LIBS: Contains a list of additional library directories that the code server searches for applications and adds to the code path; see code(3erl).
ERL_EPMD_ADDRESS: Can be set to a comma-separated list of IP addresses, in which case the epmd daemon listens only on the specified address(es) and on the loopback address (which is implicitly added to the list if it has not been specified).
ERL_EPMD_PORT: Can contain the port number to use when communicating with epmd. The default port works fine in most cases. A different port can be specified to allow nodes of independent clusters to co-exist on the same host. All nodes in a cluster must use the same epmd port number.
On Unix systems, the Erlang runtime will interpret two types of signals.
SIGUSR1: A SIGUSR1 signal forces a crash dump.
SIGTERM: A SIGTERM will produce a stop message to the init process. This is equivalent to a init:stop/0 call.
Introduced in ERTS 8.3 (Erlang/OTP 19.3)
The signal SIGUSR2 is reserved for internal usage. No other signals are handled.
The standard Erlang/OTP system can be reconfigured to change the default behavior on startup.
The .erlang startup file: When Erlang/OTP is started, the system searches for a file named .erlang in the user's home directory.
If an .erlang file is found, it is assumed to contain valid Erlang expressions. These expressions are evaluated as if they were input to the shell.
A typical .erlang file contains a set of search paths, for example:
io:format("executing user profile in HOME/.erlang\n",[]). code:add_path("/home/calvin/test/ebin"). code:add_path("/home/hobbes/bigappl-1.2/ebin"). io:format(".erlang rc finished\n",[]).
user_default and shell_default: Functions in the shell that are not prefixed by a module name are assumed to be functional objects (funs), built-in functions (BIFs), or belong to the module user_default or shell_default.
To include private shell commands, define them in a module user_default and add the following argument as the first line in the .erlang file:
code:load_abs("..../user_default").
erl: If the contents of .erlang are changed and a private version of user_default is defined, the Erlang/OTP environment can be customized. More powerful changes can be made by supplying command- line arguments in the startup script erl. For more information, see init(3erl).
epmd(1), erl_prim_loader(3erl), erts_alloc(3erl), init(3erl), application(3erl), auth(3erl), code(3erl), erl_boot_server(3erl), heart(3erl), net_kernel(3erl), make(3erl)
kubectl rollout - Manage the rollout of a resource
kubectl rollout [OPTIONS]
Manage the rollout of a resource.
Valid resource types include:
• deployments
• daemonsets
• statefulsets
# Rollback to the previous deployment kubectl rollout undo deployment/abc
# Check the rollout status of a daemonset kubectl rollout status daemonset/foo
kubectl(1), kubectl-rollout-history(1), kubectl-rollout-pause(1), kubectl-rollout-restart(1), kubectl-rollout-resume(1), kubectl-rollout-status(1), kubectl-rollout-undo(1),
SSHD(8)                    BSD System Manager's Manual                   SSHD(8)
sshd — OpenSSH daemon
sshd [-46DdeiqTt] [-C connection_spec] [-c host_certificate_file] [-E log_file] [-f config_file] [-g login_grace_time] [-h host_key_file] [-o option] [-p port] [-u len]
sshd (OpenSSH Daemon) is the daemon program for ssh(1).  It provides secure encrypted communications between two untrusted hosts over an insecure network.
sshd listens for connections from clients.  It is normally started at boot from /etc/rc.  It forks a new daemon for each incoming connection.  The forked daemons handle key exchange, encryption, authentication, command execution, and data exchange.
sshd can be configured using command-line options or a configuration file (by default sshd_config(5)); command-line options override values specified in the configuration file.  sshd rereads its configuration file when it receives a hangup signal, SIGHUP, by executing itself with the name and options it was started with, e.g. /usr/sbin/sshd.
-4      Forces sshd to use IPv4 addresses only.
-6      Forces sshd to use IPv6 addresses only.
-C connection_spec Specify the connection parameters to use for the -T extended test mode.  If provided, any Match directives in the configuration file that would apply are applied before the configuration is written to standard output.  The connection parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple -C options or as a comma-separated list.  The keywords are “addr”, “user”, “host”, “laddr”, “lport”, and “rdomain” and correspond to source address, user, resolved source host name, local address, local port number and routing domain respectively.
-c host_certificate_file Specifies a path to a certificate file to identify sshd during key exchange.  The certificate file must match a host key file specified using the -h option or the HostKey configuration directive.
-D      When this option is specified, sshd will not detach and does not become a daemon.  This allows easy monitoring of sshd.
-d      Debug mode.  The server sends verbose debug output to standard error, and does not put itself in the background.  The server also will not fork(2) and will only process one connection.  This option is only intended for debugging for the server.  Multiple -d options increase the debugging level.  Maximum is 3.
-E log_file Append debug logs to log_file instead of the system log.
-e      Write debug logs to standard error instead of the system log.
-f config_file Specifies the name of the configuration file.  The default is /etc/ssh/sshd_config.  sshd refuses to start if there is no configuration file.
-g login_grace_time Gives the grace time for clients to authenticate themselves (default 120 seconds).  If the client fails to authenticate the user within this many seconds, the server disconnects and exits.  A value of zero indicates no limit.
-h host_key_file Specifies a file from which a host key is read.  This option must be given if sshd is not run as root (as the normal host key files are normally not readable by anyone but root).  The default is /etc/ssh/ssh_host_ecdsa_key, /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key.  It is possible to have multiple host key files for the different host key algorithms.
-i      Specifies that sshd is being run from inetd(8).
-o option Can be used to give options in the format used in the configuration file.  This is useful for specifying options for which there is no separate command-line flag.  For full details of the options, and their values, see sshd_config(5).
-p port Specifies the port on which the server listens for connections (default 22).  Multiple port options are permitted.  Ports specified in the configuration file with the Port option are ignored when a command-line port is specified.  Ports specified using the ListenAddress option override command-line ports.
-q      Quiet mode.  Nothing is sent to the system log.  Normally the beginning, authentication, and termination of each connection is logged.
-T      Extended test mode.  Check the validity of the configuration file, output the effective configuration to stdout and then exit. Optionally, Match rules may be applied by specifying the connection parameters using one or more -C options.
-t      Test mode.  Only check the validity of the configuration file and sanity of the keys.  This is useful for updating sshd reliably as configuration options may change.
-u len  This option is used to specify the size of the field in the utmp structure that holds the remote host name.  If the resolved host name is longer than len, the dotted decimal value will be used instead.  This allows hosts with very long host names that overflow this field to still be uniquely identified.  Specifying -u0 indicates that only dotted decimal addresses should be put into the utmp file.  -u0 may also be used to prevent sshd from making DNS requests unless the authentication mechanism or configuration requires it.  Authentication mechanisms that may require DNS include HostbasedAuthentication and using a from="pattern-list" option in a key file.  Configuration options that require DNS include using a USER@HOST pattern in AllowUsers or DenyUsers.
The OpenSSH SSH daemon supports SSH protocol 2 only.  Each host has a host- specific key, used to identify the host.  Whenever a client connects, the daemon responds with its public host key.  The client compares the host key against its own database to verify that it has not changed.  Forward secrecy is provided through a Diffie-Hellman key agreement.  This key agreement results in a shared session key.  The rest of the session is encrypted using a symmetric cipher.  The client selects the encryption algorithm to use from those offered by the server.  Additionally, session integrity is provided through a cryptographic message authentication code (MAC).
Finally, the server and the client enter an authentication dialog.  The client tries to authenticate itself using host-based authentication, public key authentication, challenge-response authentication, or password authentication.
Regardless of the authentication type, the account is checked to ensure that it is accessible.  An account is not accessible if it is locked, listed in DenyUsers or its group is listed in DenyGroups .  The definition of a locked account is system dependent. Some platforms have their own account database (eg AIX) and some modify the passwd field ( ‘*LK*’ on Solaris and UnixWare, ‘*’ on HP-UX, containing ‘Nologin’ on Tru64, a leading ‘*LOCKED*’ on FreeBSD and a leading ‘!’ on most Linuxes).  If there is a requirement to disable password authentication for the account while allowing still public-key, then the passwd field should be set to something other than these values (eg ‘NP’ or ‘*NP*’ ).
If the client successfully authenticates itself, a dialog for preparing the session is entered.  At this time the client may request things like allocating a pseudo-tty, forwarding X11 connections, forwarding TCP connections, or forwarding the authentication agent connection over the secure channel.
After this, the client either requests an interactive shell or execution or a non-interactive command, which sshd will execute via the user's shell using its -c option.  The sides then enter session mode.  In this mode, either side may send data at any time, and such data is forwarded to/from the shell or command on the server side, and the user terminal in the client side.
When the user program terminates and all forwarded X11 and other connections have been closed, the server sends command exit status to the client, and both sides exit.
When a user successfully logs in, sshd does the following:
1.   If the login is on a tty, and no command has been specified, prints last login time and /etc/motd (unless prevented in the configuration file or by ~/.hushlogin; see the FILES section).
2.   If the login is on a tty, records login time.
3.   Checks /etc/nologin; if it exists, prints contents and quits (unless root).
4.   Changes to run with normal user privileges.
5.   Sets up basic environment.
6.   Reads the file ~/.ssh/environment, if it exists, and users are allowed to change their environment.  See the PermitUserEnvironment option in sshd_config(5).
7.   Changes to user's home directory.
8.   If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option is set, runs it; else if /etc/ssh/sshrc exists, runs it; otherwise runs xauth(1).  The “rc” files are given the X11 authentication protocol and cookie in standard input.  See SSHRC, below.
9.   Runs user's shell or command.  All commands are run under the user's login shell as specified in the system password database.
If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment files but before starting the user's shell or command.  It must not produce any output on stdout; stderr must be used instead.  If X11 forwarding is in use, it will receive the "proto cookie" pair in its standard input (and DISPLAY in its environment).  The script must call xauth(1) because sshd will not run xauth automatically to add X11 cookies.
The primary purpose of this file is to run any initialization routines which may be needed before the user's home directory becomes accessible; AFS is a particular example of such an environment.
This file will probably contain some initialization code followed by something similar to:
if read proto cookie && [ -n "$DISPLAY" ]; then if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then # X11UseLocalhost=yes echo add unix:`echo $DISPLAY | cut -c11-` $proto $cookie else # X11UseLocalhost=no echo add $DISPLAY $proto $cookie fi | xauth -q - fi
If this file does not exist, /etc/ssh/sshrc is run, and if that does not exist either, xauth is used to add the cookie.
AUTHORIZED_KEYS FILE FORMAT AuthorizedKeysFile specifies the files containing public keys for public key authentication; if this option is not specified, the default is ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2.  Each line of the file contains one key (empty lines and lines starting with a ‘#’ are ignored as comments).  Public keys consist of the following space-separated fields: options, keytype, base64-encoded key, comment.  The options field is optional.  The supported key types are:
sk-ecdsa-sha2-nistp256@openssh.com ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521 sk-ssh-ed25519@openssh.com ssh-ed25519 ssh-dss ssh-rsa
The comment field is not used for anything (but may be convenient for the user to identify the key).
Note that lines in this file can be several hundred bytes long (because of the size of the public key encoding) up to a limit of 8 kilobytes, which permits RSA keys up to 16 kilobits.  You don't want to type them in; instead, copy the id_dsa.pub, id_ecdsa.pub, id_ecdsa_sk.pub, id_ed25519.pub, id_ed25519_sk.pub, or the id_rsa.pub file and edit it.
sshd enforces a minimum RSA key modulus size of 1024 bits.
agent-forwarding Enable authentication agent forwarding previously disabled by the restrict option.
cert-authority Specifies that the listed key is a certification authority (CA) that is trusted to validate signed certificates for user authentication.
Certificates may encode access restrictions similar to these key options.  If both certificate restrictions and key options are present, the most restrictive union of the two is applied.
command="command" Specifies that the command is executed whenever this key is used for authentication.  The command supplied by the user (if any) is ignored.  The command is run on a pty if the client requests a pty; otherwise it is run without a tty.  If an 8-bit clean channel is required, one must not request a pty or should specify no-pty.  A quote may be included in the command by quoting it with a backslash.
This option might be useful to restrict certain public keys to perform just a specific operation.  An example might be a key that permits remote backups but nothing else.  Note that the client may specify TCP and/or X11 forwarding unless they are explicitly prohibited, e.g. using the restrict key option.
The command originally supplied by the client is available in the SSH_ORIGINAL_COMMAND environment variable.  Note that this option applies to shell, command or subsystem execution.  Also note that this command may be superseded by a sshd_config(5) ForceCommand directive.
If a command is specified and a forced-command is embedded in a certificate used for authentication, then the certificate will be accepted only if the two commands are identical.
environment="NAME=value" Specifies that the string is to be added to the environment when logging in using this key.  Environment variables set this way override other default environment values.  Multiple options of this type are permitted.  Environment processing is disabled by default and is controlled via the PermitUserEnvironment option.
expiry-time="timespec" Specifies a time after which the key will not be accepted.  The time may be specified as a YYYYMMDD date or a YYYYMMDDHHMM[SS] time in the system time-zone.
from="pattern-list" Specifies that in addition to public key authentication, either the canonical name of the remote host or its IP address must be present in the comma-separated list of patterns.  See PATTERNS in ssh_config(5) for more information on patterns.
In addition to the wildcard matching that may be applied to hostnames or addresses, a from stanza may match IP addresses using CIDR address/masklen notation.
The purpose of this option is to optionally increase security: public key authentication by itself does not trust the network or name servers or anything (but the key); however, if somebody somehow steals the key, the key permits an intruder to log in from anywhere in the world.  This additional option makes using a stolen key more difficult (name servers and/or routers would have to be compromised in addition to just the key).
no-agent-forwarding Forbids authentication agent forwarding when this key is used for authentication.
no-port-forwarding Forbids TCP forwarding when this key is used for authentication. Any port forward requests by the client will return an error.  This might be used, e.g. in connection with the command option.
no-pty  Prevents tty allocation (a request to allocate a pty will fail).
no-user-rc Disables execution of ~/.ssh/rc.
no-X11-forwarding Forbids X11 forwarding when this key is used for authentication. Any X11 forward requests by the client will return an error.
permitlisten="[host:]port" Limit remote port forwarding with the ssh(1) -R option such that it may only listen on the specified host (optional) and port.  IPv6 addresses can be specified by enclosing the address in square brackets.  Multiple permitlisten options may be applied separated by commas.  Hostnames may include wildcards as described in the PATTERNS section in ssh_config(5).  A port specification of * matches any port.  Note that the setting of GatewayPorts may further restrict listen addresses.  Note that ssh(1) will send a hostname of “localhost” if a listen host was not specified when the forwarding was requested, and that this name is treated differently to the explicit localhost addresses “127.0.0.1” and “::1”.
permitopen="host:port" Limit local port forwarding with the ssh(1) -L option such that it may only connect to the specified host and port.  IPv6 addresses can be specified by enclosing the address in square brackets. Multiple permitopen options may be applied separated by commas.  No pattern matching or name lookup is performed on the specified hostnames, they must be literal host names and/or addresses.  A port specification of * matches any port.
port-forwarding Enable port forwarding previously disabled by the restrict option.
principals="principals" On a cert-authority line, specifies allowed principals for certificate authentication as a comma-separated list.  At least one name from the list must appear in the certificate's list of principals for the certificate to be accepted.  This option is ignored for keys that are not marked as trusted certificate signers using the cert-authority option.
pty     Permits tty allocation previously disabled by the restrict option.
no-touch-required Do not require demonstration of user presence for signatures made using this key.  This option only makes sense for the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.
verify-required Require that signatures made using this key attest that they verified the user, e.g. via a PIN.  This option only makes sense for the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.
restrict Enable all restrictions, i.e. disable port, agent and X11 forwarding, as well as disabling PTY allocation and execution of ~/.ssh/rc.  If any future restriction capabilities are added to authorized_keys files they will be included in this set.
tunnel="n" Force a tun(4) device on the server.  Without this option, the next available device will be used if the client requests a tunnel.
user-rc Enables execution of ~/.ssh/rc previously disabled by the restrict option.
X11-forwarding Permits X11 forwarding previously disabled by the restrict option.
An example authorized_keys file:
# Comments are allowed at start of line. Blank lines are allowed. # Plain key, no restrictions ssh-rsa ... # Forced command, disable PTY and all forwarding restrict,command="dump /home" ssh-rsa ... # Restriction of ssh -L forwarding destinations permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa ... # Restriction of ssh -R forwarding listeners permitlisten="localhost:8080",permitlisten="[::1]:22000" ssh-rsa ... # Configuration for tunnel forwarding tunnel="0",command="sh /etc/netstart tun0" ssh-rsa ... # Override of restriction to allow PTY allocation restrict,pty,command="nethack" ssh-rsa ... # Allow FIDO key without requiring touch no-touch-required sk-ecdsa-sha2-nistp256@openssh.com ... # Require user-verification (e.g. PIN or biometric) for FIDO key verify-required sk-ecdsa-sha2-nistp256@openssh.com ... # Trust CA key, allow touch-less FIDO if requested in certificate cert-authority,no-touch-required,principals="user_a" ssh-rsa ...
SSH_KNOWN_HOSTS FILE FORMAT The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host public keys for all known hosts.  The global file should be prepared by the administrator (optional), and the per-user file is maintained automatically: whenever the user connects to an unknown host, its key is added to the per-user file.
Each line in these files contains the following fields: marker (optional), hostnames, keytype, base64-encoded key, comment.  The fields are separated by spaces.
The marker is optional, but if it is present then it must be one of “@cert-authority”, to indicate that the line contains a certification authority (CA) key, or “@revoked”, to indicate that the key contained on the line is revoked and must not ever be accepted.  Only one marker should be used on a key line.