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Manual Section... (5) - page: init

 

NAME

init - init daemon job configuration  

SYNOPSIS

/etc/init  

DESCRIPTION

On startup, the Upstart init(8) daemon reads its job configuration from the /etc/init directory, and watches for future changes using inotify(7).

Files in this directory must end in .conf and may also be present in sub-directories.

Each file defines a single service or task, with the name taken from its relative path within the directory without the extension. For example a job defined in /etc/init/rc-sysinit.conf is named rc-sysinit, while a job defined in /etc/init/net/apache.conf is named net/apache.

These files are plain text and should not be executable.  

Format

Each line begins with a configuration stanza and continues until either the end of the line or a line containing a closing stanza. Line breaks within a stanza are permitted within single or double quotes, or if preceeded by a blackslash.

Stanzas and their arguments are delimited by whitespace, which consists of one or more space or tab characters which are otherwise ignored unless placed within single or double quotes.

Comments begin with a `#' and continue until the end of the line. Blank lines and lines consisting only of whitespace or comments are ignored.  

Process definition

The primary use of jobs is to define services or tasks to be run by the init(8) daemon. Each job may have one or more different processes run as part of its lifecycle, with the most common known as the main process.

The main process is defined using either the exec or script stanzas, only one of which is permitted. These specify the executable or shell script that will be run when the job is considered to be running. Once this process terminates, the job stop.

All processes are run with the full job environment available as environment variables in their process.

exec COMMAND [ ARG ]...
This stanza defines the process to be run as the name of an executable on the filesystem, and zero or more arguments to be passed to it. Any special characters, e.g. quotes or `$' specified will result in the entire command being passed to a shell for expansion.

exec /usr/sbin/acpid -c $EVENTSDIR -s $SOCKET
script ... end script
This stanza defines the process to be run as a shell script that will be executed using sh(1). The -e shell option is always used, so any command that fails will terminate the script.

The script stanza appears on its own on a line, the script is everything up until the first end script stanza appearing on its own on a line.

script
    dd bs=1 if=/proc/kmsg of=$KMSGSINK
    exec /sbin/klogd -P $KMSGSINK
end script

There an additional four processes that may be run as part of the job's lifecycle. These are specified as the process name, followed by an exec or script stanza.

pre-start exec|script...
This process will be run after the job's starting(7) event has finished, but before the main process is run. It is typically used to prepare the environment, such as making necessary directories.
post-start exec|script...
This process will be run before the job's started(7) event is emitted, but after the main process has been spawned. It is typically used to send necessary commands to the main process, or to delay the started(7) event until the main process is ready to receive clients.
pre-stop exec|script...
This process is run if the job is stopped by an event listed in its stop on stanza or by the stop(8) command. It will be run before the job's stopping(7) event is emitted and before the main process is killed. It is typically used to send any necessary shutdown commands to the main process, and it may also call the start(8) command without arguments to cancel the stop.
post-stop exec|script...
This process is run after the main process has been killed and before the job's stopped(7) event is emitted. It is typically used to clean up the environment, such as removing temporary directories.

All of these process, including the main process, are optional. Services without a main process will appear to be running until they are stopped, this is commonly used to define states such as runlevels. It's quite permissable to have no main process, but to have pre-start and post-stop processes for the state.

pre-start exec ifup -a
post-stop exec ifdown -a
 

Event definition

Jobs can be manually started and stopped at any time by a system adminstrator using the. start(8) and stop(8) tools, however it is far more useful for jobs to be started and stopped automatically by the init(8) daemon when necessary.

This is done by specifying which events should cause your job to be started, and which cause your process to be stopped again.

The set of possible events is limitless, however there are a number of standard events defined by the init(8) daemon and telinit(8) tools that you will want to use.

When first started, the init(8) daemon will emit the startup(7) event. This will activate jobs that implement System V compatibility and the runlevel(7) event. As jobs are started and stopped, the init(8) daemon will emit the starting(7), started(7), stopping(7) and stopped(7) events on their behalf.

start on EVENT [[KEY=]VALUE]... [and|or...]
The start on stanza defines the set of events that will cause the job to be automatically started. Each EVENT is given by its name. Multiple events are permitted using the and & or operators, and complex expressions may be performed with parentheses (within which line breaks are permitted).

You may also match on the environment variables contained within the event by specifying the KEY and expected VALUE. If you know the order in which the variables are given to the event you may omit the KEY.

VALUE may contain wildcard matches and globs as permitted by fnmatch(3) and may expand the value of any variable defined with the env stanza.

start on started gdm or started kdm

start on device-added SUBSYSTEM=tty DEVPATH=ttyS*
stop on EVENT [[KEY=]VALUE]... [and|or...]
The stop on stanza defines the set of events that will cause the job to be automatically stopped. It has the same syntax as start on

VALUE may additionally expand the value of any variable that came from the job's start environment (either the event or the command that started it).

stop on stopping gdm or stopping kdm

stop on device-removed DEVPATH=$DEVPATH
 

Job environment

Each job is run with the environment from the events or commands that started it. In addition, you may define defaults in the job which may be overridden later and specify which environment variables are exported into the events generated for the job.

The special UPSTART_EVENTS environment variable contains the list of events that started the job, it will not be present if the job was started manually.

In addition, the pre-stop and post-stop scripts are run with the environment of the events or commands that stopped the job. THe UPSTART_STOP_EVENTS environment variable contains the list of events that stopped the job, it will not be present if the job was stopped manually.

All jobs also contain the UPSTART_JOB and UPSTART_INSTANCE environment variables, containing the name of the job and instance. These are mostly used by the initctl(8) utility to default to acting on the job the commands are called from.

env KEY=VALUE
Defines a default environment variable, the value of which may be overriden by the event or command that starts the job.
export KEY
Exports the value of an environment variable into the starting(7), started(7), stopping(7) and stopped(7) events for this job.
 

Services, tasks and respawning

Jobs are services by default. This means that the act of starting the job is considered to be finished when the job is running, and that even exiting with a zero exit status means the service will be respawned.

task
This stanza may be used to specify that the job is a task instead. This means that the act of starting the job is not considered to be finished until the job itself has been run and stopped again, but that existing with a zero exit status means the task has completed successfully and will not be respawned.

The start(8) command, and any starting(7) or stopping(7) events will block only until a service is running or until a task has finished.

respawn
A service or task with this stanza will be automatically started if it should stop abnormally. All reasons for a service stopping, except the stop(8) command itself, are considered abnormal. Tasks may exit with a zero exit status to prevent being respawned.
respawn limit COUNT INTERVAL
Respawning is subject to a limit, if the job is respawned more than COUNT times in INTERVAL seconds, it will be considered to be having deeper problems and will be stopped.

This only applies to automatic respawns and not the restart(8) command.

normal exit STATUS|SIGNAL...
Additional exit statuses or even signals may be added, if the job process terminates with any of these it will not be considered to have failed and will not be respawned.

normal exit 0 1 TERM HUP
 

Instances

By default, only one instance of any job is permitted to exist at one time. Attempting to start a job when it's already starting or running results in an error.

Multiple instances may be permitted by defining the names of those instances. If an instance with the same name is not already starting or running, a new instance will be started instead of returning an error.

instance NAME
This stanza defines the names of instances, on its own its not particularly useful since it would just define the name of the single permitted instance, however NAME expands any variable defined in the job's environment.

These will often be variables that you need to pass to the process anyway, so are an excellent way to limit the instances.

instance $CONFFILE
exec /sbin/httpd -c $CONFFILE

instance $TTY
exec /sbin/getty -8 38300 $TTY

These jobs appear in the initctl(8) output with the instance name in parentheses, and have the INSTANCE environment variable set in their events.

 

Documentation

Upstart provides several stanzas useful for documentation and external tools.

description DESCRIPTION
This stanza may contain a description of the job.

description "This does neat stuff"
author AUTHOR
This stanza may contain the author of the job, often used as a contact for bug reports.

author "Scott James Remnant <scott@netsplit.com>"
version VERSION
This stanza may contain version information about the job, such as revision control or package version number. It is not used or interpreted by init(8) in any way.

version "$Id$"
emits EVENT...
All processes on the system are free to emit their own events by using the initctl(8) tool, or by communicating directly with the init(8) daemon.

This stanza allows a job to document in its job configuration what events it emits itself, and may be useful for graphing possible transitions.

 

Process environment

Many common adjustments to the process environment, such as resource limits, may be configured directly in the job rather than having to handle them yourself.

console output|owner
By default the standard input, output and error file descriptors of jobs are connected to /dev/null

If this stanza is specified, they are connected to /dev/console instead.

console owner is special, it not only connects the job to the system console but sets the job to be the owner of the system console, which means it will receive certain signals from the kernel when special key combinations such as Control-C are pressed.

umask UMASK
A common configuration is to set the file mode creation mask for the process. UMASK should be an octal value for the mask, see umask(2) for more details.
nice NICE
Another common configuration is to adjust the process's nice value, see nice(1) for more details.
oom ADJUSTMENT|never
Normally the OOM killer regards all processes equally, this stanza advises the kernel to treat this job differently.

ADJUSTMENT may be an integer value from -16 (very unlikely to be killed by the OOM killer) up to 14 (very likely to be killed by the OOM killer). It may also be the special value never to have the job ignored by the OOM killer entirely.

chroot DIR
Runs the job's processes in a chroot(8) environment underneath DIR

Note that DIR must have all the necessary system libraries for the process to be run, often including /bin/sh

chdir DIR
Runs the job's processes with a working directory of DIR instead of the root of the filesystem.
limit LIMIT SOFT|unlimited HARD|unlimited
Sets initial system resource limits for the job's processes. LIMIT may be one of core, cpu, data, fsize, memlock, msgqueue, nice, nofile, nproc, rss, rtprio, sigpending or stack.

Limits are specified as both a SOFT value and a HARD value, both of which are integers. The special value unlimited may be specified for either.

 

Miscellaneous

kill timeout INTERVAL
Specifies the interval between sending the job's main process the SIGTERM and SIGKILL signals when stopping the running job.
expect stop
Specifies that the job's main process will raise the SIGSTOP signal to indicate that it is ready. init(8) will wait for this signal before running the job's post-start script, or considering the job to be running.

init(8) will send the process the SIGCONT signal to allow it to continue.

expect daemon
Specifies that the job's main process is a daemon, and will fork twice after being run. init(8) will follow this daemonisation, and will wait for this to occur before running the job's post-start script or considering the job to be running.

Without this stanza init(8) is unable to supervise daemon processes and will believe them to have stopped as soon as they daemonise on startup.

expect fork
Specifies that the job's main process will fork once after being run. init(8) will follow this fork, and will wait for this to occur before running the job's post-start script or considering the job to be running.

Without this stanza init(8) is unable to supervise forking processes and will believe them to have stopped as soon as they fork on startup.

 

SEE ALSO

init(8) sh(1)


 

Index

NAME
SYNOPSIS
DESCRIPTION
Format
Process definition
Event definition
Job environment
Services, tasks and respawning
Instances
Documentation
Process environment
Miscellaneous
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 15:27:47 GMT, June 11, 2010

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