diff options
author | pjd <pjd@FreeBSD.org> | 2005-08-24 17:21:38 +0000 |
---|---|---|
committer | pjd <pjd@FreeBSD.org> | 2005-08-24 17:21:38 +0000 |
commit | a5fe3401b9f1cc44c8011e8aa5cdbbe2637084e4 (patch) | |
tree | b6de69447d47fffaa83dd6300aab8b56a9a55567 /lib/libutil/pidfile.3 | |
parent | 473f777e4d124b4ed88d3eb95798889f5570e7f4 (diff) | |
download | FreeBSD-src-a5fe3401b9f1cc44c8011e8aa5cdbbe2637084e4.zip FreeBSD-src-a5fe3401b9f1cc44c8011e8aa5cdbbe2637084e4.tar.gz |
Add a family of functions for reliable pidfiles handling.
Idea from: jmg
Discussed on: arch@
Diffstat (limited to 'lib/libutil/pidfile.3')
-rw-r--r-- | lib/libutil/pidfile.3 | 227 |
1 files changed, 227 insertions, 0 deletions
diff --git a/lib/libutil/pidfile.3 b/lib/libutil/pidfile.3 new file mode 100644 index 0000000..4ae7067 --- /dev/null +++ b/lib/libutil/pidfile.3 @@ -0,0 +1,227 @@ +.\" Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org> +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd August 22, 2005 +.Dt PIDFILE 3 +.Os +.Sh NAME +.Nm pidfile_open , +.Nm pidfile_write , +.Nm pidfile_close , +.Nm pidfile_remove +.Nd library for PID files handling +.Sh LIBRARY +.Lb libutil +.Sh SYNOPSIS +.In sys/param.h +.In libutil.h +.Ft struct pidfh * +.Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr" +.Ft int +.Fn pidfile_write "struct pidfh *pfh" +.Ft int +.Fn pidfile_close "struct pidfh *pfh" +.Ft int +.Fn pidfile_remove "struct pidfh *pfh" +.Sh DESCRIPTION +The +.Nm libpidfile +library provides functions for daemons to handle file with PID. +It uses +.Xr flock 2 +to lock pidfile and detect already running daemons. +.Pp +The +.Fn pidfile_open +function opens (or creates) a file specified by +.Fa path +argument and locks it with +.Xr flock 2 +syscall. +If file can not be locked, PID of already running daemon is returned in +.Fa pidptr +argument (if it is not NULL). +The function doesn't write process' PID into the file here, so it can be +used before fork()ing and exit with proper error message when needed. +If +.Fa path +argument is NULL, +.Pa /var/run/<progname>.pid +file will be used. +.Pp +The +.Fn pidfile_write +function write process' PID into previously opened file. +.Pp +The +.Fn pidfile_close +function closes pidfile. +It should be used after daemon fork()s to start a child process. +.Pp +The +.Fn pidfile_remove +function closes and removes pidfile. +.Sh RETURN VALUES +The +.Fn pidfile_open +function return a valid pointer to a pidfh structure on success or +.Dv NULL +if an error occurs. +If an error does occur, +.Va errno +will be set. +.Rv -std pidfile_write pidfile_close pidfile_remove +.Sh EXAMPLES +The following example shows in which order those functions should be used. +.Bd -literal +struct pidfh *pfh; +pid_t otherpid, childpid; + +pfh = pidfile_open("/var/run/daemon.pid", 0644, &otherpid); +if (pfh == NULL) { + if (errno == EEXIST) + errx(EXIT_FAILURE, "Daemon already running, pid: %d.", otherpid); + /* If we cannot create pidfile from other reasons, only warn. */ + warn("Cannot open or create pidfile"); +} + +if (daemon(0, 0) == -1) { + warn("Cannot daemonize"); + pidfile_remove(pfh); + exit(EXIT_FAILURE); +} + +pidfile_write(pfh); + +for (;;) { + /* Do work. */ + childpid = fork(); + switch (childpid) { + case -1: + syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno)); + break; + case 0: + pidfile_close(pfh); + /* Do child work. */ + break; + default: + syslog(LOG_INFO, "Child %d started.", childpid); + break; + } +} + +pidfile_remove(pfh); +exit(EXIT_SUCCESS); +.Ed +.Sh ERRORS +The +.Fn pidfile_open +function will fail if: +.Bl -tag -width Er +.It Bq Er EEXIST +Some process already holds the lock on the given pidfile, which means, +daemon is already running. +.It Bq Er ENAMETOOLONG +Specified pidfile's name is too long. +.It Bq Er EINVAL +Some process already holds the lock on the given pidfile, but PID read +from there is invalid. +.El +.Pp +The +.Fn pidfile_open +function may also fail and set +.Va errno +for any errors specified for the +.Xr fstat 2 , +.Xr open 2 , +.Xr read 2 +routines. +.Pp +The +.Fn pidfile_write +function will fail if: +.Bl -tag -width Er +.It Bq Er EDOOFUS +Inproper function use. +Probably called before +.Fn pidfile_open . +.El +.Pp +The +.Fn pidfile_write +function may also fail and set +.Va errno +for any errors specified for the +.Xr fstat 2 , +.Xr ftruncate 2 , +.Xr write 2 +routines. +.Pp +The +.Fn pidfile_close +function may fail and set +.Va errno +for any errors specified for the +.Xr close 2 , +.Xr fstat 2 +routines. +.Pp +The +.Fn pidfile_remove +function will fail if: +.Bl -tag -width Er +.It Bq Er EDOOFUS +Inproper function use. +Probably called not from the process which made +.Fn pidfile_write . +.El +.Pp +The +.Fn pidfile_remove +function may also fail and set +.Va errno +for any errors specified for the +.Xr close 2 , +.Xr flock 2 , +.Xr fstat 2 , +.Xr write 2 , +.Xr unlink 2 +routines. +.Pp +.Sh SEE ALSO +.Xr flock 2 , +.Xr open 2 , +.Xr daemon 3 +.Sh AUTHORS +.An -nosplit +The +.Xr pidfile 3 +functionality is based on ideas from +.An John-Mark Gurney Aq jmg@FreeBSD.org . +.Pp +The code and manual page was written by +.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org . |