/**
* slibc — Yet another C library
* Copyright © 2015 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version. As a special exception for this
* file, you may also redistribute it and/or modify it under the terms
* of the Expat License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <sys/resource.h>
/**
* The process's environment variables.
*/
extern char** environ;
/**
* Daemonise the process. This means to:
*
* - close all file descritors except for those to
* stdin, stdout, and stderr,
*
* - remove all custom signal handlers, and apply
* the default handlers.
*
* - unblock all signals,
*
* - remove all malformatted entries in the
* environment (this not containing an '=',)
*
* - set the umask to zero, to be ensure that all
* file permissions are set as specified,
*
* - change directory to '/', to ensure that the
* process does not block any mountpoint from being
* unmounted,
*
* - fork to become a background process,
*
* - temporarily become a session leader to ensure
* that the process does not have a controlling
* terminal.
*
* - fork again to become a child of the daemon
* supervisor, (subreaper could however be in the
* say, so one should not merely rely on this when
* writing a daemon supervisor,) (the first child
* shall exit after this,)
*
* - create, exclusively, a PID file to stop the daemon
* to be being run twice concurrently, and to let
* the daemon supervicer know the process ID of the
* daemon,
*
* - redirect stdin and stdout to /dev/null,
* as well as stderr if it is currently directed
* to a terminal, and
*
* - exit in the original process to let the daemon
* supervisor know that the daemon has been
* initialised.
*
* Before calling this function, you should remove any
* environment variable that could negatively impact
* the runtime of the process.
*
* After calling this function, you should remove
* unnecessary privileges.
*
* Do not try do continue the process in failure unless
* you make sure to only do this in the original process.
* But not that things will not necessarily be as when
* you make the function call. The process can have become
* partially deamonised.
*
* @etymology (Daemonise) the process!
*
* @param name The name of the daemon. Use a hardcoded value,
* not the process name. Must not be `NULL`.
* @param flags Flags to modify the behaviour of the function.
* A bitwise OR combination of the constants:
* - `DAEMONISE_NO_CLOSE`
* - `DAEMONISE_NO_SIG_DFL`
* - `DAEMONISE_KEEP_SIGMASK`
* - `DAEMONISE_KEEP_ENVIRON`
* - `DAEMONISE_KEEP_UMASK`
* - `DAEMONISE_NO_PID_FILE`
* - `DAEMONISE_KEEP_STDERR`
* - `DAEMONISE_CLOSE_STDERR`
* - `DAEMONISE_KEEP_STDIN`
* - `DAEMONISE_KEEP_STDOUT`
* @return Zero on success, -1 on error.
*
* @throws EEXIST The PID file already exists on the system.
* Unless your daemon supervisor removs old
* PID files, this could mean that the daemon
* has exited without removing the PID file.
* @throws Any error specified for signal(3).
* @throws Any error specified for sigemptyset(3).
* @throws Any error specified for sigprocmask(3).
* @throws Any error specified for chdir(3).
* @throws Any error specified for pipe(3).
* @throws Any error specified for dup2(3).
* @throws Any error specified for fork(3).
* @throws Any error specified for setsid(3).
* @throws Any error specified for open(3).
*
* @since Always.
*/
int daemonise(const char* name, int flags) /* TODO user-private daemons */
{
#define t(...) do { if (__VA_ARGS__) goto fail; } while (0)
struct rlimit rlimit;
int pipe_rw[2] = { -1, -1 };
sigset_t set;
char* r;
char* w;
int i, closeerr, fd = -1;
int saved_errno;
/* Validate flags. */
if (flags & ~1023)
return errno = EINVAL, -1;
if (flags & DAEMONISE_KEEP_STDERR)
if (flags & DAEMONISE_CLOSE_STDERR)
return errno = EINVAL, -1;
/* Close all files except stdin, stdou, and stderr. */
if ((flags & DAEMONISE_NO_CLOSE) == 0)
{
if (getrlimit(RLIMIT_NOFILE, &rlimit))
rlimit.rlim_cur = 4 << 10;
for (i = 3; (rlim_t)i < rlimit.rlim_cur; i++)
/* File descriptors with numbers above and including
* `rlimit.rlim_cur` cannot be created. They cause EBADF. */
close(i);
}
/* Reset all signal handlers. */
if ((flags & DAEMONISE_NO_SIG_DFL) == 0)
for (i = 1; i < _NSIG; i++)
t (signal(i, SIG_DFL) == SIG_ERR);
/* Set signal mask. */
if ((flags & DAEMONISE_KEEP_SIGMASK) == 0)
{
t (sigemptyset(&set));
t (sigprocmask(SIG_SETMASK, &set, NULL));
}
/* Remove malformatted environment entires. */
if (((flags & DAEMONISE_KEEP_ENVIRON) == 0) && (environ != NULL))
{
for (r = w = environ; *r; r++)
if (strchr(*r, '=')) /* It happens that this is not the case! (Thank you PAM!) */
*w++ = *r;
*w = NULL;
}
/* Zero umask. */
if ((flags & DAEMONISE_KEEP_UMASK) == 0)
umask(0);
/* Change current working directory to '/'. */
t (chdir("/"));
/* Create a channel for letting the original process know when to exit. */
if (pipe(pipe_rw))
t ((pipe_rw[0] = pipe_rw[1] = -1));
t (dup2(pipe_rw[0], 10) == -1);
close(pipe_rw[0]);
pipe_rw[0] = 10;
t (dup2(pipe_rw[1], 11) == -1);
close(pipe_rw[1]);
pipe_rw[1] = 11;
/* Become a background process. */
t (pid = fork(), pid == -1);
close(pipe_rw[!!pid]), pipe_rw[!!pid] = 1;
if (pid)
exit(read(pipe_rw[0], &b, (size_t)1) <= 0);
/* Temporarily become session leader. */
t (setsid() == -1);
/* Fork again. */
t (pid = fork(), pid == -1);
if (pid > 0)
exit(0);
/* Create PID file. */
if (flags & DAEMONISE_NO_PID_FILE)
goto no_pid_file;
pidpath = alloca(sizeof("/run/.pid") + strlen(name) * sizeof(char));
stpcpy(stpcpy(stpcpy(pidpath, "/run/"), name), ".pid");
fd = open(pidpath, O_WRONLY | O_CREAT | O_EXCL, 0644);
t (fd == -1);
pid = getpid();
t (dprintf(fd, "%lli\n", (long long int)pid)) < 0;
t (close(fd) && (errno != EINTR));
no_pid_file:
/* Redirect to '/dev/null'. */
if (flags & DAEMONISE_KEEP_STDERR)
closeerr = 0;
else if (flags & DAEMONISE_CLOSE_STDERR)
closeerr = 1;
else
closeerr = (isatty(2) || (errno == EBADF));
t (fd = open("/dev/null", O_RDWR), fd == -1);
if ((flags & DAEMONISE_KEEP_STDIN) == 0) if (fd != 0) close(0);
if ((flags & DAEMONISE_KEEP_STDOUT) == 0) if (fd != 1) close(1);
if (closeerr) if (fd != 2) close(2);
if ((flags & DAEMONISE_KEEP_STDIN) == 0) t (dup2(fd, 0) == -1);
if ((flags & DAEMONISE_KEEP_STDOUT) == 0) t (dup2(fd, 1) == -1);
if (closeerr) t (dup2(fd, 2) == -1);
if (fd > 2)
close(fd);
fd = -1;
/* We are done! Let the original process exit. */
if ((write(pipe_rw[1], &b, (size_t)1) <= 0) ||
(close(pipe_rw[1]) && (errno != EINTR)))
{
if (flags & DAEMONISE_KEEP_STDERR)
return -1;
abort(); /* Do not overcomplicate things, just abort in this unlikely event. */
}
return 0;
fail:
saved_errno = err;
if (pipe_rw[0] >= 0) close(pipe_rw[0]);
if (pipe_rw[1] >= 0) close(pipe_rw[1]);
if (fd >= 0) close(fd);
errno = saved_errno;
return -1;
}
