NAME
pidfile,
pidfile_lock, pidfile_read,
pidfile_clean —
write a daemon pid file
LIBRARY
library “libutil”
SYNOPSIS
#include
<util.h>
int
pidfile(const
char *path);
pid_t
pidfile_lock(const
char *path);
pid_t
pidfile_read(const
char *path);
int
pidfile_clean(void);
DESCRIPTION
pidfile()
and
pidfile_lock()
create and lock a file containing the process ID of the calling program. The
pid file can be used as a quick reference if the process needs to be sent a
signal. The pid file is truncated and removed automatically when the program
exits, unless the program receives a fatal signal.
If path is NULL or a
plain basename (a name containing no directory components), the pid file is
created in the /var/run directory. The file name has
the form /var/run/basename.pid. The basename part is
either the value of path if it was not
NULL, or the program name as returned by
getprogname(3) otherwise.
If path is an absolute or relative path (i.e. it contains the ‘/’ character), the pid file is created in the provided location.
If called with a new path,
pidfile()
and
pidfile_lock()
will remove the old pid file.
The pid file is truncated, so these functions can be called multiple times and allow a child process to take over the lock.
pidfile_read()
will read the last pid file created, or specified by
path, and return the process ID it contains.
pidfile_clean()
will ftruncate(2),
close(2), and
unlink(2) the last opening pid file if, and only if, the current
process wrote it. This function should be called if the program needs to
call _exit(2) (such as from a signal handler) and needs to clean up the
pid file.
RETURN VALUES
pidfile() and
pidfile_clean() returns 0 on success and -1 on
failure.
pidfile_lock() returns 0 on success.
Otherwise, the process ID who owns the lock is returned and if that cannot
be derived then -1 is returned.
pidfile_read() returns the process ID if
known, otherwise -1.
ERRORS
The pidfile() and
pidfile_lock() functions will fail if:
- [
EEXIST] - Some process already holds the lock on the given pid file, meaning that a daemon is already running.
- [
ENAMETOOLONG] - Specified pidfile's name is too long.
SEE ALSO
HISTORY
The pidfile() function call appeared in
NetBSD 1.5. Support for creating pid files in any
arbitrary path was added in NetBSD 6.0.
The pidfile_lock(),
pidfile_read(), and
pidfile_clean() function calls appeared in
NetBSD 8.
CAVEATS
pidfile() and
pidfile_lock() use
atexit(3) to ensure the pid file is cleaned at program exit. However,
programs that use the
_exit(2) function (for example, in signal handlers) will not trigger
this behaviour and should call pidfile_clean().
Like-wise, if the program creates a pid file before
fork(2)ing a child to take over, it should use the
_exit(2) function instead of returning or using the
exit(3) function to ensure the pid file is not cleaned.