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)

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

       None.

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

       None.

ENVIRONMENT VARIABLES         top

       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.

ASYNCHRONOUS EVENTS         top

       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.

EXTENDED DESCRIPTION         top

       None.

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.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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         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 $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 &

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       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)

COPYRIGHT         top

       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)