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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 |
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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.1‐2017, 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.1‐2017, 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.1‐2017.
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.1‐2017.
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.1‐2017, Chapter 8,
Environment Variables
The System Interfaces volume of POSIX.1‐2017, signal(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 NOHUP(1P)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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