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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
NOHUP(1P) POSIX Programmer's Manual NOHUP(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
nohup — invoke a utility immune to hangups
nohup utility [argument...]
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 standard input is associated with a terminal, the nohup utility
may redirect standard input from an unspecified file.
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 standard error is a terminal and standard output is open but is
not a terminal, all output written by the named utility to its
standard error shall be redirected to the same open file description
as the standard output. If standard error is a terminal and standard
output either is a terminal or is closed, the same output shall
instead be appended to the end of the nohup.out file as described
above.
None.
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
Section 2.14, 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.
Not used.
None.
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 POSIX.1‐2008, 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
POSIX.1‐2008, Chapter 8, Environment Variables.
The nohup utility shall take the standard action for all signals
except that SIGHUP shall be ignored.
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.
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 written by the named utility is appended to the file nohup.out
(or $HOME/nohup.out), if the conditions hold as described in the
DESCRIPTION.
None.
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.
Default.
The following sections are informative.
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.
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' </dev/null
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 POSIX.1‐2008.
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 POSIX.1‐2008.
Historical versions of nohup did not affect standard input, but that
causes problems in the common scenario where the user logs into a
system, types the command:
nohup make &
at the prompt, and then logs out. If standard input is not affected
by nohup, the login session may not terminate for quite some time,
since standard input remains open until make exits. To avoid this
problem, POSIX.1‐2008 allows implementations to redirect standard
input if it is a terminal. Since the behavior is implementation-
defined, portable applications that may run into the problem should
redirect standard input themselves. For example, instead of:
nohup make &
an application can invoke:
nohup make </dev/null &
None.
Chapter 2, Shell Command Language, sh(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables
The System Interfaces volume of POSIX.1‐2008, signal(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 NOHUP(1P)