xenial (1) nohup.1posix.gz

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PROLOG
       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
       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.1‐2008, 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
       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.1‐2008.

       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
       None.


SEE ALSO
       Chapter 2, Shell Command Language, sh

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables

       The System Interfaces volume of POSIX.1‐2008, signal()


       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 .

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