07-07-2008
How to find if a process a daemon ?
I have a scenario where I need to find if a process is a daemon process or not. This check needs to be done from within the process. I know there are no direct API's to do so. I have explored these options.
1. ctermid() - this can be unsuccessful as per the man pages
2. int devtty; if ((devtty = open ("/dev/tty", O_RDWR)) < 0) then it is a daemon. Are there any other cases, where this may not be true ?
3. Since setsid() is used to detach from a terminal, perhaps getsid() can be used to check for process group leader and session leader.
4. Look if parent pid is 1 or not. Can a daemon process have a ppid other than 1 ?
Are there more options ? I dont know if there is a best way to do this, but what would be the most appropriate way ?
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SETSID(2) Linux Programmer's Manual SETSID(2)
NAME
setsid - creates a session and sets the process group ID
SYNOPSIS
#include <unistd.h>
pid_t setsid(void);
DESCRIPTION
setsid() creates a new session if the calling process is not a process group leader. The calling process is the leader of the new session,
the process group leader of the new process group, and has no controlling tty. The process group ID and session ID of the calling process
are set to the PID of the calling process. The calling process will be the only process in this new process group and in this new session.
RETURN VALUE
On success, the (new) session ID of the calling process is returned. On error, (pid_t) -1 is returned, and errno is set to indicate the
error.
ERRORS
EPERM The process group ID of any process equals the PID of the calling process. Thus, in particular, setsid() fails if the calling
process is already a process group leader.
CONFORMING TO
SVr4, POSIX.1-2001.
NOTES
A child created via fork(2) inherits its parent's session ID. The session ID is preserved across an execve(2).
A process group leader is a process with process group ID equal to its PID. In order to be sure that setsid() will succeed, fork(2) and
_exit(2), and have the child do setsid().
SEE ALSO
getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7)
COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2008-12-03 SETSID(2)