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Diffstat (limited to 'lib/libutil/pidfile.3')
| -rw-r--r-- | lib/libutil/pidfile.3 | 297 |
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diff --git a/lib/libutil/pidfile.3 b/lib/libutil/pidfile.3 new file mode 100644 index 0000000..d5e2470 --- /dev/null +++ b/lib/libutil/pidfile.3 @@ -0,0 +1,297 @@ +.\" 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 February 8, 2012 +.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 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" +.Ft int +.Fn pidfile_fileno "struct pidfh *pfh" +.Sh DESCRIPTION +The +.Nm pidfile +family of functions allows daemons to handle PID files. +It uses +.Xr flopen 3 +to lock a pidfile and detect already running daemons. +.Pp +The +.Fn pidfile_open +function opens (or creates) a file specified by the +.Fa path +argument and locks it. +If +.Fa pidptr +argument is not +.Dv NULL +and file can not be locked, the function will use it to store a PID of an +already running daemon or +.Li -1 +in case daemon did not write its PID yet. +The function does not write process' PID into the file here, so it can be +used before +.Fn fork Ns ing +and exit with a proper error message when needed. +If the +.Fa path +argument is +.Dv NULL , +.Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid +file will be used. +The +.Fn pidfile_open +function sets the O_CLOEXEC close-on-exec flag when opening the pidfile. +.Pp +The +.Fn pidfile_write +function writes process' PID into a previously opened file. +The file is truncated before write, so calling the +.Fn pidfile_write +function multiple times is supported. +.Pp +The +.Fn pidfile_close +function closes a pidfile. +It should be used after daemon +.Fn fork Ns s +to start a child process. +.Pp +The +.Fn pidfile_remove +function closes and removes a pidfile. +.Pp +The +.Fn pidfile_fileno +function returns the file descriptor for the open pidfile. +.Sh RETURN VALUES +The +.Fn pidfile_open +function returns a valid pointer to a +.Vt pidfh +structure on success, or +.Dv NULL +if an error occurs. +If an error occurs, +.Va errno +will be set. +.Pp +.Rv -std pidfile_write pidfile_close pidfile_remove +.Pp +The +.Fn pidfile_fileno +function returns the low-level file descriptor. +It returns +.Li -1 +and sets +.Va errno +if a NULL +.Vt pidfh +is specified, or if the pidfile is no longer open. +.Sh EXAMPLES +The following example shows in which order these functions should be used. +Note that it is safe to pass +.Dv NULL +to +.Fn pidfile_write , +.Fn pidfile_remove , +.Fn pidfile_close +and +.Fn pidfile_fileno +functions. +.Bd -literal +struct pidfh *pfh; +pid_t otherpid, childpid; + +pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid); +if (pfh == NULL) { + if (errno == EEXIST) { + errx(EXIT_FAILURE, "Daemon already running, pid: %jd.", + (intmax_t)otherpid); + } + /* If we cannot create pidfile from other reasons, only warn. */ + warn("Cannot open or create pidfile"); + /* + * Eventhough pfh is NULL we can continue, as the other pidfile_* + * function can handle such situation by doing nothing except setting + * errno to EDOOFUS. + */ +} + +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 %jd started.", (intmax_t)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, meaning that a +daemon is already running. +If +.Fa pidptr +argument is not +.Dv NULL +the function will use it to store a PID of an already running daemon or +.Li -1 +in case daemon did not write its PID yet. +.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 , +and +.Xr read 2 +calls. +.Pp +The +.Fn pidfile_write +function will fail if: +.Bl -tag -width Er +.It Bq Er EDOOFUS +Improper 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 , +and +.Xr write 2 +calls. +.Pp +The +.Fn pidfile_close +function may fail and set +.Va errno +for any errors specified for the +.Xr close 2 +and +.Xr fstat 2 +calls. +.Pp +The +.Fn pidfile_remove +function will fail if: +.Bl -tag -width Er +.It Bq Er EDOOFUS +Improper 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 fstat 2 , +.Xr write 2 , +and +.Xr unlink 2 +system calls and the +.Xr flopen 3 +library function. +.Pp +The +.Fn pidfile_fileno +function will fail if: +.Bl -tag -width Er +.It Bq Er EDOOFUS +Improper function use. +Probably called not from the process which used +.Fn pidfile_open . +.El +.Sh SEE ALSO +.Xr open 2 , +.Xr daemon 3 , +.Xr flopen 3 +.Sh AUTHORS +.An -nosplit +The +.Nm pidfile +functionality is based on ideas from +.An John-Mark Gurney Aq Mt jmg@FreeBSD.org . +.Pp +The code and manual page was written by +.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org . |
