NAME
pidfile —
write a daemon pid
file
LIBRARY
System Utilities Library (libutil, -lutil)
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
flock(2),
atexit(3)
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.