NAME
nohup - invoke a utility immune to hangups
SYNOPSIS
nohup utility [argument...]
DESCRIPTION
The nohup utility shall invoke the utility named by the utility operand
with arguments supplied as the argument operands. At the time the named
utility is invoked, the SIGHUP signal shall be set to be ignored.
If the standard output is a terminal, all output written by the named
utility to its standard output shall be appended to the end of the file
nohup.out in the current directory. If nohup.out cannot be created or
opened for appending, the output shall be appended to the end of the
file nohup.out in the directory specified by the HOME environment
variable. If neither file can be created or opened for appending,
utility shall not be invoked. If a file is created, the file’s
permission bits shall be set to S_IRUSR | S_IWUSR.
If the standard error is a terminal, all output written by the named
utility to its standard error shall be redirected to the same file
descriptor as the standard output.
OPTIONS
None.
OPERANDS
The following operands shall be supported:
utility
The name of a utility that is to be invoked. If the utility
operand names any of the special built-in utilities in Special
Built-In Utilities , the results are undefined.
argument
Any string to be supplied as an argument when invoking the
utility named by the utility operand.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
nohup:
HOME Determine the pathname of the user’s home directory: if the
output file nohup.out cannot be created in the current
directory, the nohup utility shall use the directory named by
HOME to create the file.
LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.
LC_CTYPE
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of
LC_MESSAGES .
PATH Determine the search path that is used to locate the utility to
be invoked. See the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
ASYNCHRONOUS EVENTS
The nohup utility shall take the standard action for all signals except
that SIGHUP shall be ignored.
STDOUT
If the standard output is not a terminal, the standard output of nohup
shall be the standard output generated by the execution of the utility
specified by the operands. Otherwise, nothing shall be written to the
standard output.
STDERR
If the standard output is a terminal, a message shall be written to the
standard error, indicating the name of the file to which the output is
being appended. The name of the file shall be either nohup.out or
$HOME/nohup.out.
OUTPUT FILES
If the standard output is a terminal, all output written by the named
utility to the standard output and standard error is appended to the
file nohup.out, which is created if it does not already exist.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
126 The utility specified by utility was found but could not be
invoked.
127 An error occurred in the nohup utility or the utility specified
by utility could not be found.
Otherwise, the exit status of nohup shall be that of the utility
specified by the utility operand.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The command, env, nice, nohup, time, and xargs utilities have been
specified to use exit code 127 if an error occurs so that applications
can distinguish "failure to find a utility" from "invoked utility
exited with an error indication". The value 127 was chosen because it
is not commonly used for other meanings; most utilities use small
values for "normal error conditions" and the values above 128 can be
confused with termination due to receipt of a signal. The value 126 was
chosen in a similar manner to indicate that the utility could be found,
but not invoked. Some scripts produce meaningful error messages
differentiating the 126 and 127 cases. The distinction between exit
codes 126 and 127 is based on KornShell practice that uses 127 when all
attempts to exec the utility fail with [ENOENT], and uses 126 when any
attempt to exec the utility fails for any other reason.
EXAMPLES
It is frequently desirable to apply nohup to pipelines or lists of
commands. This can be done by placing pipelines and command lists in a
single file; this file can then be invoked as a utility, and the nohup
applies to everything in the file.
Alternatively, the following command can be used to apply nohup to a
complex command:
nohup sh -c ’complex-command-line’
RATIONALE
The 4.3 BSD version ignores SIGTERM and SIGHUP, and if ./nohup.out
cannot be used, it fails instead of trying to use $HOME/nohup.out.
The csh utility has a built-in version of nohup that acts differently
from the nohup defined in this volume of IEEE Std 1003.1-2001.
The term utility is used, rather than command, to highlight the fact
that shell compound commands, pipelines, special built-ins, and so on,
cannot be used directly. However, utility includes user application
programs and shell scripts, not just the standard utilities.
Historical versions of the nohup utility use default file creation
semantics. Some more recent versions use the permissions specified here
as an added security precaution.
Some historical implementations ignore SIGQUIT in addition to SIGHUP;
others ignore SIGTERM. An early proposal allowed, but did not require,
SIGQUIT to be ignored. Several reviewers objected that nohup should
only modify the handling of SIGHUP as required by this volume of
IEEE Std 1003.1-2001.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language , sh , the System Interfaces volume of
IEEE Std 1003.1-2001, signal()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .