- NetBSD Manual Pages
PIDFILE(3) NetBSD Library Functions Manual PIDFILE(3)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
pidfile, pidfile_lock, pidfile_read, pidfile_clean -- write a daemon pid
System Utilities Library (libutil, -lutil)
pidfile(const char *path);
pidfile_lock(const char *path);
pidfile_read(const char *path);
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 com-
ponents), 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
If path is an absolute or relative path (i.e. it contains the `/' charac-
ter), 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 open-
ing pid file if, and only if, the current process wrote it. This func-
tion 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.
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.
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.
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.
pidfile() and pidfile_lock() use atexit(3) to ensure the pid file is
cleaned at program exit. However, programs that use the _exit(2) func-
tion (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.
NetBSD 9.2 April 10, 2016 NetBSD 9.2