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#include <libutil.h>
The pidfile_open() function opens (or creates) a file specified by the path argument and locks it. If pidptr argument is not NULL and file can not be locked, the function will use it to store a PID of an already running daemon or -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 fork()ing and exit with a proper error message when needed. If the path argument is NULL, /var/run/< progname > .pid file will be used. The pidfile_open() function sets the O_CLOEXEC close-on-exec flag when opening the pidfile.
The pidfile_write() function writes process' PID into a previously opened file. The file is truncated before write, so calling the pidfile_write() function multiple times is supported.
The pidfile_close() function closes a pidfile. It should be used after daemon fork()s to start a child process.
The pidfile_remove() function closes and removes a pidfile.
The pidfile_fileno() function returns the file descriptor for the open pidfile.
The pidfile_write, pidfile_closeand pidfile_remove functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
The pidfile_fileno() function returns the low-level file descriptor. It returns -1 and sets errno if a NULL pidfh is specified, or if the pidfile is no longer open.
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"); /* * Even though 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);
[EEXIST] | |
Some process already holds the lock on the given pidfile, meaning that a daemon is already running. If pidptr argument is not NULL the function will use it to store a PID of an already running daemon or -1 in case daemon did not write its PID yet. | |
[ENAMETOOLONG] | |
Specified pidfile's name is too long. | |
[EINVAL] | |
Some process already holds the lock on the given pidfile, but PID read from there is invalid. | |
The pidfile_open() function may also fail and set errno for any errors specified for the fstat(2), open(2), and read(2) calls.
The pidfile_write() function will fail if:
[EDOOFUS] | |
Improper function use. Probably called before pidfile_open(). | |
The pidfile_write() function may also fail and set errno for any errors specified for the fstat(2), ftruncate(2), and write(2) calls.
The pidfile_close() function may fail and set errno for any errors specified for the close(2) and fstat(2) calls.
The pidfile_remove() function will fail if:
[EDOOFUS] | |
Improper function use. Probably called not from the process which made pidfile_write(). | |
The pidfile_remove() function may also fail and set errno for any errors specified for the close(2), fstat(2), write(2), and unlink(2) system calls and the flopen(3) library function.
The pidfile_fileno() function will fail if:
[EDOOFUS] | |
Improper function use. Probably called not from the process which used pidfile_open(). | |
The code and manual page was written by Pawel Jakub Dawidek <Mt pjd@FreeBSD.org>.
PIDFILE (3) | May 10, 2020 |
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