man-pages/man1p/nohup.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "NOHUP" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" nohup 
.SH NAME
nohup \- invoke a utility immune to hangups
.SH SYNOPSIS
.LP
\fBnohup\fP \fIutility\fP \fB[\fP\fIargument\fP\fB...\fP\fB]\fP
.SH DESCRIPTION
.LP
The \fInohup\fP utility shall invoke the utility named by the \fIutility\fP
operand with arguments supplied as the
\fIargument\fP operands. At the time the named \fIutility\fP is invoked,
the SIGHUP signal shall be set to be ignored.
.LP
If the standard output is a terminal, all output written by the named
\fIutility\fP to its standard output shall be appended to
the end of the file \fBnohup.out\fP in the current directory. If \fBnohup.out\fP
cannot be created or opened for appending, the
output shall be appended to the end of the file \fBnohup.out\fP in
the directory specified by the \fIHOME\fP environment
variable. If neither file can be created or opened for appending,
\fIutility\fP shall not be invoked. If a file is created, the
file's permission bits shall be set to S_IRUSR | S_IWUSR.
.LP
If the standard error is a terminal, all output written by the named
\fIutility\fP to its standard error shall be redirected to
the same file descriptor as the standard output.
.SH OPTIONS
.LP
None.
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIutility\fP
The name of a utility that is to be invoked. If the \fIutility\fP
operand names any of the special built-in utilities in \fISpecial
Built-In Utilities\fP , the results are undefined.
.TP 7
\fIargument\fP
Any string to be supplied as an argument when invoking the utility
named by the \fIutility\fP operand.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fInohup\fP:
.TP 7
\fIHOME\fP
Determine the pathname of the user's home directory: if the output
file \fBnohup.out\fP cannot be created in the current
directory, the \fInohup\fP utility shall use the directory named by
\fIHOME\fP to create the file.
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPATH\fP
Determine the search path that is used to locate the utility to be
invoked. See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Chapter 8, Environment Variables.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
The \fInohup\fP utility shall take the standard action for all signals
except that SIGHUP shall be ignored.
.SH STDOUT
.LP
If the standard output is not a terminal, the standard output of \fInohup\fP
shall be the standard output generated by the
execution of the \fIutility\fP specified by the operands. Otherwise,
nothing shall be written to the standard output.
.SH STDERR
.LP
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
\fBnohup.out\fP or \fB$HOME/nohup.out\fP.
.SH OUTPUT FILES
.LP
If the standard output is a terminal, all output written by the named
\fIutility\fP to the standard output and standard error
is appended to the file \fBnohup.out\fP, which is created if it does
not already exist.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
126
The utility specified by \fIutility\fP was found but could not be
invoked.
.TP 7
127
An error occurred in the \fInohup\fP utility or the utility specified
by \fIutility\fP could not be found.
.sp
.LP
Otherwise, the exit status of \fInohup\fP shall be that of the utility
specified by the \fIutility\fP operand.
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fIcommand\fP, \fIenv\fP, \fInice\fP, \fInohup\fP, \fItime\fP,
and \fIxargs\fP 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
\fIexec\fP the utility fail with [ENOENT], and uses 126 when any attempt
to \fIexec\fP the utility fails for any other
reason.
.SH EXAMPLES
.LP
It is frequently desirable to apply \fInohup\fP 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 \fInohup\fP applies to everything in the
file.
.LP
Alternatively, the following command can be used to apply \fInohup\fP
to a complex command:
.sp
.RS
.nf

\fBnohup sh -c '\fP\fIcomplex-command-line\fP\fB'
\fP
.fi
.RE
.SH RATIONALE
.LP
The 4.3 BSD version ignores SIGTERM and SIGHUP, and if \fB./nohup.out\fP
cannot be used, it fails instead of trying to use
\fB$HOME/nohup.out\fP.
.LP
The \fIcsh\fP utility has a built-in version of \fInohup\fP that acts
differently from the \fInohup\fP defined in this volume
of IEEE\ Std\ 1003.1-2001.
.LP
The term \fIutility\fP is used, rather than \fIcommand\fP, to highlight
the fact that shell compound commands, pipelines,
special built-ins, and so on, cannot be used directly. However, \fIutility\fP
includes user application programs and shell
scripts, not just the standard utilities.
.LP
Historical versions of the \fInohup\fP utility use default file creation
semantics. Some more recent versions use the
permissions specified here as an added security precaution.
.LP
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
\fInohup\fP should only modify the handling of SIGHUP as
required by this volume of IEEE\ Std\ 1003.1-2001.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIShell Command Language\fP , \fIsh\fP , the System Interfaces
volume of IEEE\ Std\ 1003.1-2001, \fIsignal\fP()
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .