'\" et

.TH NOHUP "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

nohup

\(em invoke a utility immune to hangups

.SH SYNOPSIS

.LP

.nf

nohup \fIutility \fB[\fIargument\fR...\fB]\fR

.fi

.SH DESCRIPTION

The

.IR nohup

utility shall invoke the utility named by the

.IR utility

operand with arguments supplied as the

.IR argument

operands. At the time the named

.IR utility

is invoked, the SIGHUP signal shall be set to be ignored.

.P

If standard input is associated with a terminal, the

.IR nohup

utility may redirect standard input from an unspecified file.

.P

If the standard output is a terminal, all output written by the named

.IR utility

to its standard output shall be appended to the end of the file

.BR nohup.out

in the current directory. If

.BR nohup.out

cannot be created or opened for appending, the output shall be appended

to the end of the file

.BR nohup.out

in the directory specified by the

.IR HOME

environment variable. If neither file can be created or opened for

appending,

.IR utility

shall not be invoked. If a file is created, the file's permission bits

shall be set to S_IRUSR | S_IWUSR.

.P

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

.BR nohup.out

file as described above.

.SH OPTIONS

None.

.SH OPERANDS

The following operands shall be supported:

.IP "\fIutility\fR" 10

The name of a utility that is to be invoked. If the

.IR utility

operand names any of the special built-in utilities in

.IR "Section 2.14" ", " "Special Built-In Utilities",

the results are undefined.

.IP "\fIargument\fR" 10

Any string to be supplied as an argument when invoking the utility

named by the

.IR utility

operand.

.SH STDIN

Not used.

.SH "INPUT FILES"

None.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR nohup :

.IP "\fIHOME\fP" 10

Determine the pathname of the user's home directory: if the output

file

.BR nohup.out

cannot be created in the current directory, the

.IR nohup

utility shall use the directory named by

.IR HOME

to create the file.

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_CTYPE\fP" 10

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).

.IP "\fILC_MESSAGES\fP" 10

.br

Determine the locale that should be used to affect the format and

contents of diagnostic messages written to standard error.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.IP "\fIPATH\fP" 10

Determine the search path that is used to locate the utility to be

invoked. See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables".

.SH "ASYNCHRONOUS EVENTS"

The

.IR nohup

utility shall take the standard action for all signals except that

SIGHUP shall be ignored.

.SH STDOUT

If the standard output is not a terminal, the standard output of

.IR nohup

shall be the standard output generated by the execution of the

.IR utility

specified by the operands. Otherwise, nothing shall be written to the

standard output.

.SH 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

.BR nohup.out

or

.BR $HOME/nohup.out .

.SH "OUTPUT FILES"

Output written by the named utility is appended to the file

.BR nohup.out

(or

.BR $HOME/nohup.out ),

if the conditions hold as described in the DESCRIPTION.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

The following exit values shall be returned:

.IP 126 8

The utility specified by

.IR utility

was found but could not be invoked.

.IP 127 8

An error occurred in the

.IR nohup

utility or the utility specified by

.IR utility

could not be found.

.P

Otherwise, the exit status of

.IR nohup

shall be that of the utility specified by the

.IR utility

operand.

.SH "CONSEQUENCES OF ERRORS"

Default.

.LP

.IR "The following sections are informative."

.SH "APPLICATION USAGE"

The

.IR command ,

.IR env ,

.IR nice ,

.IR nohup ,

.IR time ,

and

.IR 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

.IR exec

the utility fail with

.BR [ENOENT] ,

and uses 126 when any attempt to

.IR exec

the utility fails for any other reason.

.SH EXAMPLES

It is frequently desirable to apply

.IR 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

.IR nohup

applies to everything in the file.

.P

Alternatively, the following command can be used to apply

.IR nohup

to a complex command:

.sp

.RS 4

.nf

\fB

nohup sh \(mic '\fIcomplex-command-line\fP' 

.fi \fR

.P

.RE

.SH RATIONALE

The 4.3 BSD version ignores SIGTERM and SIGHUP, and if

.BR ./nohup.out

cannot be used, it fails instead of trying to use

.BR $HOME/nohup.out .

.P

The

.IR csh

utility has a built-in version of

.IR nohup

that acts differently from the

.IR nohup

defined in this volume of POSIX.1\(hy2008.

.P

The term

.IR utility

is used, rather than

.IR command ,

to highlight the fact that shell compound commands, pipelines, special

built-ins, and so on, cannot be used directly.

However,

.IR utility

includes user application programs and shell scripts, not just the

standard utilities.

.P

Historical versions of the

.IR nohup

utility use default file creation semantics. Some more recent versions

use the permissions specified here as an added security precaution.

.P

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

.IR nohup

should only modify the handling of SIGHUP as required by this volume of POSIX.1\(hy2008.

.P

Historical versions of

.IR nohup

did not affect standard input, but that causes problems in the common

scenario where the user logs into a system, types the command:

.sp

.RS 4

.nf

\fB

nohup make &

.fi \fR

.P

.RE

.P

at the prompt, and then logs out. If standard input is not affected by

.IR nohup ,

the login session may not terminate for quite some time, since standard

input remains open until

.IR make

exits. To avoid this problem, POSIX.1\(hy2008 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:

.sp

.RS 4

.nf

\fB

nohup make &

.fi \fR

.P

.RE

.P

an application can invoke:

.sp

.RS 4

.nf

\fB

nohup make 

.fi \fR

.P

.RE

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "Chapter 2" ", " "Shell Command Language",

.IR "\fIsh\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables"

.P

The System Interfaces volume of POSIX.1\(hy2008,

.IR "\fIsignal\fR\^(\|)"

.SH COPYRIGHT

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 .