nohup(1p) — Linux manual page


NOHUP(1P)               POSIX Programmer's Manual              NOHUP(1P)

PROLOG         top

       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.

NAME         top

       nohup — invoke a utility immune to hangups

SYNOPSIS         top

       nohup utility [argument...]

DESCRIPTION         top

       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.

OPTIONS         top


OPERANDS         top

       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.

STDIN         top

       Not used.

INPUT FILES         top



       The following environment variables shall affect the execution of

       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).

                 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.

STDOUT         top

       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         top

       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         top

       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.



EXIT STATUS         top

       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.



       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

EXAMPLES         top

       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

RATIONALE         top

       The 4.3 BSD version ignores SIGTERM and SIGHUP, and if
       ./nohup.out cannot be used, it fails instead of trying to use

       The csh utility has a built-in version of nohup that acts
       differently from the nohup defined in this volume of

       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 &



SEE ALSO         top

       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)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                         NOHUP(1P)