DAEMON(8)                                                            DAEMON(8)

       daemon - run a process detached from the current session

       daemon [-cf] [-p pidfile] [-u user[:group]] utility [arguments]
       daemon -h
       daemon -V

       Daemon's positional parameter utility is the path execve(2)'d to create
       the new detached process.  The new background process  is  the  session
       leader  of a new session, see setsid(2).  Thus the HUP signal delivered
       at the end of the current session is not delivered to the task.

       The task may still be ended via a signal.  To that end, the new process
       ID  may  be recorded in pidfile, thus allowing signal deliver to termi-
       nate the task with an explict kill(1).  The process may also be located
       via pgrep(1), or signaled via pkill(1).

       If the program is called as daemon then no options are forced.

              Change the current working directory to the root of the filesys-
              tem before executing utility.

              Redirect standard input, output and error to /dev/null.

              Print only the standard help message.

       -p pidfile
              Write new process ID to this file,  delete  on  failure.   Don't
              start the utility if the process ID in pidfile is presently run-
              ning.  Specification of dash (-) as the pidfile is an  extension
              of  the program which builds a default name from the basename of
              the utility under /var/run.

       -u user[:group]
              Drop credentials to this login before  utility  execution.   Any
              group  specified is set by a call to setgid(2) after the call to
              initgroups(3).   The  original  credentials   must   allow   the
              setuid(2)  to  succeed  (viz.  usually only the superuser can do
              this).  The empty user is mapped to "nobody".

              Show only version information and exit.

       daemon sleep 1000
              Push a sleep(1) command in its own session the  background,  but
              don't track the process ID.

       daemon sleeep 1000
              The misspelling of sleep(1) produces a useful error to stderr:
                   daemon: execvp: sleeep: No such file or directory
              This is not true for nohup(1) which puts the error in nohup.out.

       daemon -u nobody /usr/local/libexec/unixstats -p113
              Run the PEG data collector unixstats as login nobody.  Of course
              the change of user must be done as the superuser.

       daemon -u nobody:sample /usr/local/libexec/unixstats -p113
              Same  as  the previous, but run the collector as login nobody in
              group sample.

       daemon -c -p /var/run/dealer.pid -u house /usr/local/libexec/dealer
              Run the dealer program  as  login  house  with  a  pid  file  in
              /var/run/dealer.pid to prevent multiple instances.

       daemon -c -p - -u house /usr/local/libexec/dealer
              Same as the above command, but let daemon build pidfile.

       pkill -QUIT -F /var/run/dealer.pid -U house
              Safely  terminate any running dealer process.  By including both
              the pidfile and the login name we limit pkill's  actions  enough
              that we are unlikely to shoot an innocent (unrelated) process.

       daemon -V
              See the informative version output, which includes the printf(3)
              format used to construct default pidfile names.

       The addition of a group is non-portable, so it is not listed in the on-
       line help output.

       The  flock(2)  system call the BSD version of this program used to lock
       pidfile is, sadly, not portable (anymore).  This version only locks the
       pidfile for updates.

       A pidfile left-over from a previous system boot may contain the process
       ID of an unrelated process, which will keep daemon from starting a  new
       instance.  Always clean /var/run at system boot to prevent this bug.

       A  pidfile  with  a  non-numeric string in it prevents daemon from ever
       starting a process, or updating the file.  This is also a feature.  For
       example  I  use  the  string  "#locked"  to denote an explicitly locked
       facility.  A file with only white-space in it is still going  to  block
       the process, so check for just a newline in it.

       The  exit  codes  are  not from sysexits(3).  They are 1 for for failed
       system calls, 2 for failure to build or update the pidfile, and 3  when
       the  process  in the pidfile is running or the file is removed while we
       are updating it.

       KS Braunsdorf with liberal consultation from the FreeBSD version.
       NonPlayer Character Guild
       op at ksb dot npc guild dot orgspam-me-not

       sh(1), nohup(1), op(1l), unixstats(7l), pkill(1)

                                     LOCAL                           DAEMON(8)