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.Dd December 27, 2023
.Dt DAEMON 8
.Os
.Sh NAME
.Nm daemon
.Nd run detached from the controlling terminal
.Sh SYNOPSIS
.Nm
.Op Fl cfHrS
.Op Fl p Ar child_pidfile
.Op Fl P Ar supervisor_pidfile
.Op Fl t Ar title
.Op Fl u Ar user
.Op Fl m Ar output_mask
.Op Fl o Ar output_file
.Op Fl s Ar syslog_priority
.Op Fl T Ar syslog_tag
.Op Fl l Ar syslog_facility
.Op Fl R Ar restart_delay_seconds
.Ar command arguments ...
.Sh DESCRIPTION
The
.Nm
utility detaches itself from the controlling terminal and
executes the program specified by its arguments.
Privileges may be lowered to the specified user.
The output of the daemonized process may be redirected to syslog and to a
log file.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl c , Fl -change-dir
Change the current working directory to the root
.Pq Dq Pa / .
.It Fl f , Fl -close-fds
Redirect standard input, standard output and standard error to
.Pa /dev/null .
When this option is used together with any of the options related to file
or syslog output, the standard file descriptors are first redirected to
.Pa /dev/null ,
then stdout and/or stderr is redirected to a file or to syslog as
specified by the other options.
.It Fl H , Fl -sighup
Close
.Pa output_file
and re-open it when signal
.Dv SIGHUP
is received, for interoperability with
.Xr newsyslog 1
and similar log rotation / archival mechanisms.  If
.Fl -output-file
is not specified, this flag is ignored.
.It Fl l , Fl -syslog-facility Ar syslog_facility
These facilities are accepted:
.Cm auth , authpriv , console , cron , daemon ,
.Cm ftp , kern , lpr , mail , news , ntp , security ,
.Cm syslog , user , uucp ,
and
local facilities from
.Cm local0
to
.Cm local7 .
The default is
.Cm daemon .
.It Fl m , Fl -output-mask Ar output_mask
Redirect output from the child process stdout
.Pq Cm 1 ,
stderr
.Pq Cm 2 ,
or both
.Pq Cm 3 .
This value specifies what is sent to syslog and the log file.
The default is
.Cm 3 .
.It Fl o , Fl -output-file Ar output_file
Append output from the daemonized process to
.Pa output_file .
If the file does not exist, it is created with permissions 0600.
When this option is used together with options
.Fl -change-dir
and
.Fl -sighup
the absolute path needs to be provided to ensure
.Nm
can re-open the file after a
.Dv SIGHUP .
.It Fl P , Fl -supervisor-pidfile Ar supervisor_pidfile
Write the ID of the
.Nm
process into the
.Ar supervisor_pidfile
using the
.Xr pidfile 3
functionality.
The program is executed in a spawned child process while the
.Nm
waits until it terminates to keep the
.Ar supervisor_pidfile
locked and removes it after the process exits.
The
.Ar supervisor_pidfile
owner is the user who runs the
.Nm
regardless of whether the
.Fl -user
option is used or not.
.It Fl p , Fl -child-pidfile Ar child_pidfile
Write the ID of the created process into the
.Ar child_pidfile
using the
.Xr pidfile 3
functionality.
The program is executed in a spawned child process while the
.Nm
waits until it terminates to keep the
.Ar child_pidfile
locked and removes it after the process exits.
The
.Ar child_pidfile
owner is the user who runs the
.Nm
regardless of whether the
.Fl -user
option is used or not.
.It Fl R , Fl -restart-delay Ar restart_delay_seconds
Supervise and restart the program after the specified delay
if it has been terminated.
Valid values are 1-31536000 (up to 1 year).
.It Fl r , Fl -restart
Supervise and restart the program after a one-second delay if it has
been terminated.
.It Fl S , Fl -syslog
Enable syslog output.
This is implicitly applied if other syslog parameters are provided.
The default values are daemon, notice, and daemon for facility, priority, and
tag, respectively.
.It Fl s , Fl -syslog-priority Ar syslog_priority
These priorities are accepted:
.Cm emerg , alert , crit , err , warning ,
.Cm notice , info ,
and
.Cm debug .
The default is
.Cm notice .
.It Fl T , Fl -syslog-tag Ar syslog_tag
Set the tag which is appended to all syslog messages.
The default is
.Cm daemon .
.It Fl t , Fl -title Ar title
Set the title for the daemon process.
The default is the daemonized invocation.
.It Fl u , Fl -user Ar user
Login name of the user to execute the program under.
Environment variables
.Ev HOME , USER ,
and
.Ev SHELL
are set accordingly.
Requires adequate superuser privileges.
.El
.Pp
If any of the options
.Fl -child-pidfile ,
.Fl -output-mask ,
.Fl -restart ,
.Fl -restart-delay ,
.Fl -supervisor-pidfile ,
.Fl -syslog ,
.Fl -syslog-facility
.Fl -syslog-priority ,
.Fl -syslog-tag ,
or
.Fl -output ,
are specified, the program is executed in a spawned child process.
The
.Nm
waits until it terminates to keep the pid file(s) locked and removes them
after the process exits or restarts the program.
In this case if the monitoring
.Nm
receives software termination signal
.Pq Dv SIGTERM
it forwards it to the
spawned process.
Normally it will cause the child to exit, remove the pidfile(s)
and then terminate.
.Pp
If neither file or syslog output are selected, all output is redirected to the
.Nm
process and written to stdout.
The
.Fl -close-fds
option may be used to suppress the stdout output completely.
.Pp
The
.Fl -supervisor-pidfile
option is useful combined with the
.Fl -restart
option as
.Ar supervisor_pidfile
contains the ID of the supervisor
not the child.
This is especially important if you use
.Fl -restart
in an rc script as the
.Fl -child-pidfile
option will give you the child's ID to signal when you attempt to
stop the service, causing
.Nm
to restart the child.
.Sh EXIT STATUS
The
.Nm
utility exits 1 if an error is returned by the
.Xr daemon 3
library routine, 2 if
.Ar child_pidfile
or
.Ar supervisor_pidfile
is requested, but cannot be opened, 3 if process is already running (pidfile
exists and is locked), 4 if
.Ar syslog_priority
is not accepted, 5 if
.Ar syslog_facility
is not accepted, 6 if
.Ar output_mask
is not within the accepted range, 7 if
.Ar output_file
cannot be opened for appending, and otherwise 0.
.Sh DIAGNOSTICS
If the command cannot be executed, an error message is printed to
standard error.
The exact behavior depends on the logging parameters and the
.Fl -close-fds
flag.
.Sh SEE ALSO
.Xr nohup 1 ,
.Xr setregid 2 ,
.Xr setreuid 2 ,
.Xr daemon 3 ,
.Xr exec 3 ,
.Xr pidfile 3 ,
.Xr termios 4 ,
.Xr tty 4
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 4.7 .