daemonize(1) User Manuals daemonize(1)NAMEdaemonize - run a program as a Unix daemon
SYNOPSISdaemonize [-a] [-c directory] [-e stderr] [-o stdout] [-p pidfile] [-l
lockfile] [-u user] [-v] path [arg] ...
DESCRIPTIONdaemonize runs a command as a Unix daemon. As defined in W. Richard
Stevens' 1990 book, Unix Network Programming (Addison-Wesley, 1990), a
daemon is “a process that executes `in the background' (i.e., without
an associated terminal or login shell) either waiting for some event to
occur, or waiting to perform some specified task on a periodic basis.”
Upon startup, a typical daemon program will:
o Close all open file descriptors (especially standard input, standard
output and standard error)
o Change its working directory to the root filesystem, to ensure that
it doesn't tie up another filesystem and prevent it from being
unmounted
o Reset its umask value
o Run in the background (i.e., fork)
o Disassociate from its process group (usually a shell), to insulate
itself from signals (such as HUP) sent to the process group
o Ignore all terminal I/O signals
o Disassociate from the control terminal (and take steps not to reac‐
quire one)
o Handle any SIGCLD signals
Most programs that are designed to be run as daemons do that work for
themselves. However, you'll occasionally run across one that does not.
When you must run a daemon program that does not properly make itself
into a true Unix daemon, you can use daemonize to force it to run as a
true daemon.
OPTIONS-a Append to the output files, rather than overwriting them (which
is the default). Only applicable if -e and/or -o are specified.
-c directory
Specifies the directory to which to change before running the
program. Defaults to "/". The choice for this option is impor‐
tant. The file system containing the daemon's working directory
cannot be unmounted while the daemon is running. That's why most
daemons are careful to use a working directory on the root file
system.
-e stderr
Redirect standard error to the specified file, instead of
"/dev/null".
Warning: Be careful where you redirect the output! The file sys‐
tem containing the open file cannot be unmounted as long as the
file is open. For best results, make sure that this output file
is on the same file system as the daemon's working directory.
(See the -c option.)
-E name=value
Add an environment variable to the environment the daemon will
see. The parameter must be of the form name=value. This parame‐
ter may be specified multiple times.
-o stdout
Redirect standard output to the specified file, instead of
"/dev/null".
Warning: Be careful where you redirect the output! The file sys‐
tem containing the open file cannot be unmounted as long as the
file is open. For best results, make sure that this output file
is on the same file system as the daemon's working directory.
(See the -c option.)
-p pidfile
Causes daemonize to write the numeric process ID (PID) of the
running daemon to the specified file. This option is useful when
the program being daemonized doesn't create its own PID file.
-l lockfile
Single-instance checking. Causes daemonize to ensure that no
more than one instance of the daemon is running by placing an
exclusive lock on given lockfile. If another process already has
a lock on the lockfile, daemonize exits.
It is possible to use the pidfile as the lock file (e.g., "-p
/var/run/foo -l /var/run/foo"), though typical daemons use separate
files.
NOTE: If the executed program decides to close all file descriptors,
the single-instance locking will not work, since the lock depends on an
open file descriptor. (The operating system kernel removes the lock
once the process holding the lock closes the file or exits.) Normal
processes that do not daemonize themselves do not usually close all
file descriptors.
-u user
Run the program as the specified user. This option only works if
daemonize is invoked by the superuser. Note: For obvious rea‐
sons, it's very dangerous to install daemonize as a setuid-to-
root executable. For that reason, daemonize will refuse to run
if it detects that it has been installed that way.
-v Cause daemonize to write verbose messages to standard error,
telling what it's doing as it daemonizes the program.
NOTES
If the host operating system provides the daemon(3) library routine,
daemonize will use it. Otherwise, daemonize uses its own version of
daemon(3). This choice is made at compile time. (BSD 4.4-derived oper‐
ating systems tend to provide their own daemon(3) routine.)
FreeBSD 5.0 introduced a daemon(1) command that is similar to, but less
functional, than daemonize.
LICENSE
This program released under a BSD-style license. For more details, con‐
sult the LICENSE file accompanying the source distribution, or visit
"http://software.clapper.org/daemonize/LICENSE".
SEE ALSOdaemon(3), setsid(2), flock(2)daemonize Home Page: http://software.clapper.org/daemonize/
AUTHOR
Brian M. Clapper, bmc <at> clapper <dot> org
CONTRIBUTORS
Support for the -e and -o options is based on a patch submitted by Tim
Starling (tstarling <at> wikimedia <dot> org).
Support for the -l option is based on a patch submitted by Yakov Lerner
(iler.ml <at> gmail <dot> com).
Unix August 2006 daemonize(1)
