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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 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
       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
                 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
       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 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.

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 standard output generated by the execution of the utility
       specified by the operands. Otherwise, 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
       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
       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 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
       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
       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 &

FUTURE DIRECTIONS
       None.

SEE ALSO
       Chapter _2, Shell Command Language, sh

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables

       The System Interfaces volume of POSIX.1-2017, signal()

COPYRIGHT
       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(1)
