NAME

svsh - Process supervision shell for daemontools/perp/s6/runit

SYNOPSIS

        # from the command line
        $ svsh --suite perp --basedir /etc/services

        # run one specific command and exit
        $ svsh --suite runit --basedir /var/services restart nginx

DESCRIPTION

svsh is a command line shell for process supervision suites of the daemontools family. Currently, it supports daemontools, perp, s6 and runit. It provides a unified interface allowing easy inspection and manipulation of services (i.e. processes) managed by supported supervision suites.

svsh does not require any configurations or changes to your suite's service directories; just point it at a base directory and you immediately get a usable shell, listing all services and their statuses, and accepting commands to perform on them.

The shell provides a very simple syntax that is easy to remember, far simpler than the particular syntax of the underlying supervision suite. Instead of having to execute perpctl -b /services q nginx to restart an nginx service running from /services/nginx, just execute restart nginx. Couldn't be simpler. Want to send a HUP signal to all services whose names begin with "worker"? just execute signal hup worker*.

svsh is inspired by supervisord's supervisorctl shell. I've attempted to provide a similar syntax and feature set.

OPTIONS

-s, --suite

The supervision suite managing the base directory. Either daemontools, perp, s6 or runit. If not provided, the SVSH_SUITE environment variable will be checked. An error will be raised if no suite is defined.

-d, --basedir

Base directory of services supervised by the supervision suite. If not provided, the SVSH_BASE environment variable will be checked, and if not set, the default base directory of the selected suite will be used. Check the documentation of the specific suite class for its default directory. If no directory is found, an error will be raised.

-b, --bindir

If the supervision suite's tools are not in the environment PATH variable, you can provide the directory where they are located (e.g. /usr/local/bin).

-c, --collapse

Collapse multi-process services to one line in status. See "COLLAPSE" for more details. This can be changed from inside the shell too.

COMMANDS

The following commands are provided by svsh. Note that some suites do not support all commands.

status

Prints a list of all services, their statuses (up, down, etc.), uptimes (or downtimes) and process IDs. This command is automatically executed upon initialization of the shell.

start service, ...

Starts a list of one or more services, if they are not already up.

        svsh> start nginx haproxy

stop service, ...

Stops a list of one or more services. The services stopped will not be restarted.

        svsh> stop nginx haproxy

restart service, ...

Restarts a list of one or more services. Generally, this means sending a QUIT signal to the services, which should cause them to shutdown and be restarted by the supervisor.

        svsh> restart nginx haproxy

signal sig service, ...

Send a UNIX signal to a list of one or more services. The name of the signal can be lowercase or uppercase, and may include the prefix "SIG".

        svsh> signal term nginx
        svsh> signal SIGUSR1 haproxy

rescan

Alias: update.

Causes the supervision suite to rescan the base directory for new or removed services.

fg service

"Moves" a service to the foreground, so that its output streams (at least standard output, possibly standard error) are printed on screen. In reality, it determines where the process' log file is located, and tails it with tail -f. See "LOG INSPECTION" for more details, as this is a complicated subject.

        svsh> fg nginx

terminate

Alias: shutdown.

Terminate the supervision suite. This will cause all services managed by the supervisor to terminate as well.

toggle option

Toggles a shell option on or off. Currently, only the collapse option is supported. The status command will be automatically called after toggling the option.

        svsh> toggle collapse

help [ command ]

Prints help information. Can also provide information about specific commands.

        svsh> help signal

quit

Alias: exit.

Quits the shell.

ADVANCED FEATURES AND IMPORTANT INFORMATION

LOG INSPECTION

All of the supported supervision suites do not enforce a logging scheme on managed services. While all of them provide a logging tool (daemontools provides multilog, perp provides tinylog and sissylog; s6 provides s6-log; runit provides svlogd), none of them enforce their usage. It is actually not uncommon among users of these suites to use a logging tool provided by one suite for services managed by another one. This means it is hard for an external program such as svsh to determine where log files are stored, if at all.

Currently, svsh will attempt to find the log file of a service by checking the pid of the associated log process, and if (and only if) that process is one of the supported loggers (multilog, tinylog, s6-log or svlogd), it will try to find the file descriptor used by that process under /proc/<pid>/fd. As long as your services are being logged by one of these tools, svsh should be able to tail their log files when the fg command is used. However, if the log file is being rotated while it is being tailed, behavior is currently undefined (will probably stop working until the command is run again).

HISTORY

svsh provides bash-like history so you can use your up arrow key to cycle back through past commands, or use Ctrl+R to search your history. The history file is saved under the name .svsh_history under the home directory of the running user (~/.svsh_history).

Note that history is saved only when the shell is properly terminated, such as with the quit command. Ctrl+C will not trigger history saving.

It is highly recommended to install Term::ReadLine::Gnu for proper history support.

AUTOCOMPLETION

svsh provides autocompletion for all its commands. Tap the tab key at any moment while typing in commands and arguments, and svsh will attempt to autocomplete your current word, or display a list if multiple options are available. Again, Term::ReadLine::Gnu is recommended for better autocompletion.

WILDCARDS

svsh makes it easy to manipulate multiple services at once. Wildcards are supported by the start, stop, restart and signal commands. If, for example, you have several services whose names start with "worker", you can stop them all by executing stop worker*. Wildcards are also supported at the beginning of the name, so signal term *d will send a TERM signal to all services whose names end with "d".

        svsh> status
           process |     status | duration |   pid
          worker-1 |         up |    9813s | 25984
          worker-2 |         up |    9813s | 25976
          worker-3 |         up |    4393s | 2990

        svsh> stop worker*

        svsh> status
           process |     status | duration |   pid
          worker-1 |       down |       2s |     -
          worker-2 |       down |       2s |     -
          worker-3 |       down |       2s |     -

COLLAPSE

Often times you would like to run a certain service with X number of identical processes. None of the supervision suites have any mechanism to allow this (none that I know of at least), apart from creating identical copies of a service directory for every process needed. While svsh can't help you with that, it provides a nice feature for collapsing these identical services in the output of the "status" command to just one line. This can be very useful with lots of multi-process services.

Currently, svsh determines multi-process services if their names are postfixed with a dash and a number. For example, if you have a service called worker that you need 3 processes of which to run, you can create worker-1, worker-2 and worker-3 service directories. If the collapse option is on, svsh will collapse all of these into just one line, under the name status.

        svsh> status
           process |     status | duration |   pid
          worker-1 |         up |    9813s | 25984
          worker-2 |         up |    9813s | 25976
          worker-3 |         up |    4393s | 2990

        svsh> toggle collapse
           process |     status | duration |   pid
            worker |       3 up |    9850s |     -

This feature combines well with the "WILDCARDS" feature.

Hopefully, future versions will find a more generic way of identifying multi-process services.

CONFIGURATION AND ENVIRONMENT

svsh requires no configuration files or environment variables.

DEPENDENCIES

svsh depends on the following modules:

For proper history and autocompletion support, and generally a better working shell, it is recommended to install Term::ReadLine::Gnu.

INCOMPATIBILITIES

None reported.

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to bug-Svsh@rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Svsh.

SUPPORT

You can find documentation for this module with the perldoc command.

        perldoc svsh

You can also look for information at:

AUTHOR

Ido Perlmuter <ido at ido50 dot net>.

Thanks to the guys at the supervision mailing list, especially Colin Booth, for helping out with suggestions and information.

LICENSE AND COPYRIGHT

Copyright (c) 2015, Ido Perlmuter ido at ido50 dot net.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either version 5.8.1 or any later version. See perlartistic and perlgpl.

The full text of the license can be found in the LICENSE file included with this module.

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

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