NOHUP(1) User Commands NOHUP(1)

NAME

nohup - run a command immune to hangups

SYNOPSIS

/usr/bin/nohup command [argument]...


/usr/bin/nohup -p [-Fa] pid [pid]...


/usr/bin/nohup -g [-Fa] gpid [gpid]...


/usr/xpg4/bin/nohup command [argument]...

DESCRIPTION

The nohup utility invokes the named command with the arguments supplied.
When the command is invoked, nohup arranges for the SIGHUP signal to be
ignored by the process.


When invoked with the -p or -g flags, nohup arranges for processes
already running as identified by a list of process IDs or a list of
process group IDs to become immune to hangups.


The nohup utility can be used when it is known that command takes a long
time to run and the user wants to log out of the terminal. When a shell
exits, the system sends its children SIGHUP signals, which by default
cause them to be killed. All stopped, running, and background jobs
ignores SIGHUP and continue running, if their invocation is preceded by
the nohup command or if the process programmatically has chosen to ignore
SIGHUP.

/usr/bin/nohup
Processes run by /usr/bin/nohup are immune to
SIGHUP (hangup) and SIGQUIT (quit) signals.


/usr/bin/nohup -p [-Fa]
Processes specified by ID are made immune to
SIGHUP and SIGQUIT, and all output to the
controlling terminal is redirected to
nohup.out. If -F is specified, nohup forces
control of each process. If -a is specified,
nohup changes the signal disposition of SIGHUP
and SIGQUIT even if the process has installed
a handler for either signal.


/usr/bin/nohup -g [-Fa]
Every process in the same process group as the
processes specified by ID are made immune to
SIGHUP and SIGQUIT, and all output to the
controlling terminal is redirected to
nohup.out. If -F is specified, nohup forces
control of each process. If -a is specified,
nohup changes the signal disposition of SIGHUP
and SIGQUIT even if the process has installed
a handler for either signal.


/usr/xpg4/bin/nohup
Processes run by /usr/xpg4/bin/nohup are
immune to SIGHUP.

The nohup utility does not arrange to make
processes immune to a SIGTERM (terminate)
signal, so unless they arrange to be immune to
SIGTERM or the shell makes them immune to
SIGTERM, they will receive it.

If nohup.out is not writable in the current
directory, output is redirected to
$HOME/nohup.out. If a file is created, the
file has read and write permission (600. See
chmod(1). If the standard error is a terminal,
it is redirected to the standard output,
otherwise it is not redirected. The priority
of the process run by nohup is not altered.

OPTIONS

The following options are supported:

-a
Always changes the signal disposition of target processes. This
option is valid only when specified with -p or -g.


-F
Force. Grabs the target processes even if another process has
control. This option is valid only when specified with -p or -g.


-g
Operates on a list of process groups. This option is not valid with
-p.


-p
Operates on a list of processes. This option is not valid with -g.

OPERANDS

The following operands are supported:

pid
A decimal process ID to be manipulated by nohup -p.


pgid
A decimal process group ID to be manipulated by nohup -g.


command
The name of a command that is to be invoked. If the command
operand names any of the special shell_builtins(1) utilities,
the results are undefined.


argument
Any string to be supplied as an argument when invoking the
command operand.

USAGE

Caution should be exercised when using the -F flag. Imposing two
controlling processes on one victim process can lead to chaos. Safety is
assured only if the primary controlling process, typically a debugger,
has stopped the victim process and the primary controlling process is
doing nothing at the moment of application of the proc tool in question.

EXAMPLES

Example 1: Applying nohup to pipelines or command lists

It is frequently desirable to apply nohup to pipelines or lists of
commands. This can be done only by placing pipelines and command lists in
a single file, called a shell script. One can then issue:


example$ nohup sh file


and the nohup applies to everything in file. If the shell script file is
to be executed often, then the need to type sh can be eliminated by
giving file execute permission.


Add an ampersand and the contents of file are run in the background with
interrupts also ignored (see sh(1)):


example$ nohup file &

Example 2: Applying nohup -p to a process

example$ long_running_command &
example$ nohup -p `pgrep long_running_command`

Example 3: Applying nohup -g to a process group

example$ make &
example$ ps -o sid -p $$
SID
81079
example$ nohup -g `pgrep -s 81079 make`

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment variables
that affect the execution of nohup: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,
PATH, NLSPATH, and PATH.

HOME
Determine the path name of the user's home directory: if the
output file nohup.out cannot be created in the current directory,
the nohup command uses the directory named by HOME to create the
file.

EXIT STATUS

The following exit values are returned:

126
command was found but could not be invoked.


127
An error occurred in nohup, or command could not be found


Otherwise, the exit values of nohup are those of the command operand.

FILES

nohup.out
The output file of the nohup execution if standard
output is a terminal and if the current directory is
writable.


$HOME/nohup.out
The output file of the nohup execution if standard
output is a terminal and if the current directory is
not writable.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

/usr/bin/nohup


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|CSI | Enabled |
+---------------+-----------------+

/usr/xpg4/bin/nohup


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|CSI | Enabled |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+

SEE ALSO

batch(1), chmod(1), csh(1), ksh(1), nice(1), pgrep(1), proc(1), ps(1),
sh(1), shell_builtins(1), signal(3C), proc(5), attributes(7), environ(7),
standards(7)

WARNINGS

If you are running the Korn shell (ksh(1)) as your login shell, and have
nohup'ed jobs running when you attempt to log out, you are warned with
the message:

You have jobs running.


You need to log out a second time to actually log out. However, your
background jobs continues to run.

NOTES

The C-shell (csh(1)) has a built-in command nohup that provides immunity
from SIGHUP, but does not redirect output to nohup.out. Commands
executed with `&' are automatically immune to HUP signals while in the
background.


nohup does not recognize command sequences. In the case of the following
command,

example$ nohup command1; command2


the nohup utility applies only to command1. The command,

example$ nohup (command1; command2)


is syntactically incorrect.

June 19, 2006 NOHUP(1)