NOHUP(P) NOHUP(P)
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 stan-
dard 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 stan-
dard 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 direc-
tory 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, Inter-
nationalization 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 interna-
tionalization 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 argu-
ments).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diag-
nostic 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 stan-
dard output generated by the execution of the utility specified by the operands. Other-
wise, 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 stan-
dard 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 util-
ity" 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, util-
ity 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, sig-
nal()
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
POSIX 2003 NOHUP(P)
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