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)