1NOHUP(1P) POSIX Programmer's Manual NOHUP(1P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 nohup — invoke a utility immune to hangups
13
15 nohup utility [argument...]
16
18 The nohup utility shall invoke the utility named by the utility operand
19 with arguments supplied as the argument operands. At the time the named
20 utility is invoked, the SIGHUP signal shall be set to be ignored.
21 If standard input is associated with a terminal, the nohup utility may
23 redirect standard input from an unspecified file.
24 If the standard output is a terminal, all output written by the named
26 utility to its standard output shall be appended to the end of the file
27 nohup.out in the current directory. If nohup.out cannot be created or
28 opened for appending, the output shall be appended to the end of the
29 file nohup.out in the directory specified by the HOME environment vari‐
30 able. If neither file can be created or opened for appending, utility
31 shall not be invoked. If a file is created, the file's permission bits
32 shall be set to S_IRUSR | S_IWUSR.
33 If standard error is a terminal and standard output is open but is not
35 a terminal, all output written by the named utility to its standard
36 error shall be redirected to the same open file description as the
37 standard output. If standard error is a terminal and standard output
38 either is a terminal or is closed, the same output shall instead be
39 appended to the end of the nohup.out file as described above.
40
42 None.
43
45 The following operands shall be supported:
46 utility The name of a utility that is to be invoked. If the utility
48 operand names any of the special built-in utilities in Sec‐
49 tion 2.14, Special Built-In Utilities, the results are unde‐
50 fined.
51 argument Any string to be supplied as an argument when invoking the
53 utility named by the utility operand.
54
56 Not used.
57
59 None.
60
62 The following environment variables shall affect the execution of
63 nohup:
64 HOME Determine the pathname of the user's home directory: if the
66 output file nohup.out cannot be created in the current direc‐
67 tory, the nohup utility shall use the directory named by HOME
68 to create the file.
69 LANG Provide a default value for the internationalization vari‐
71 ables that are unset or null. (See the Base Definitions vol‐
72 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
73 ables for the precedence of internationalization variables
74 used to determine the values of locale categories.)
75 LC_ALL If set to a non-empty string value, override the values of
77 all the other internationalization variables.
78 LC_CTYPE Determine the locale for the interpretation of sequences of
80 bytes of text data as characters (for example, single-byte as
81 opposed to multi-byte characters in arguments).
82 LC_MESSAGES
84 Determine the locale that should be used to affect the format
85 and contents of diagnostic messages written to standard
86 error.
87 NLSPATH Determine the location of message catalogs for the processing
89 of LC_MESSAGES.
90 PATH Determine the search path that is used to locate the utility
92 to be invoked. See the Base Definitions volume of
93 POSIX.1‐2017, Chapter 8, Environment Variables.
94
96 The nohup utility shall take the standard action for all signals except
97 that SIGHUP shall be ignored.
98
100 If the standard output is not a terminal, the standard output of nohup
101 shall be the standard output generated by the execution of the utility
102 specified by the operands. Otherwise, nothing shall be written to the
103 standard output.
104
106 If the standard output is a terminal, a message shall be written to the
107 standard error, indicating the name of the file to which the output is
108 being appended. The name of the file shall be either nohup.out or
109 $HOME/nohup.out.
110
112 Output written by the named utility is appended to the file nohup.out
113 (or $HOME/nohup.out), if the conditions hold as described in the
114 DESCRIPTION.
115
117 None.
118
120 The following exit values shall be returned:
121 126 The utility specified by utility was found but could not be
123 invoked.
124 127 An error occurred in the nohup utility or the utility specified
126 by utility could not be found.
127 Otherwise, the exit status of nohup shall be that of the utility speci‐
129 fied by the utility operand.
130
132 Default.
133 The following sections are informative.
135
137 The command, env, nice, nohup, time, and xargs utilities have been
138 specified to use exit code 127 if an error occurs so that applications
139 can distinguish ``failure to find a utility'' from ``invoked utility
140 exited with an error indication''. The value 127 was chosen because it
141 is not commonly used for other meanings; most utilities use small val‐
142 ues for ``normal error conditions'' and the values above 128 can be
143 confused with termination due to receipt of a signal. The value 126 was
144 chosen in a similar manner to indicate that the utility could be found,
145 but not invoked. Some scripts produce meaningful error messages differ‐
146 entiating the 126 and 127 cases. The distinction between exit codes 126
147 and 127 is based on KornShell practice that uses 127 when all attempts
148 to exec the utility fail with [ENOENT], and uses 126 when any attempt
149 to exec the utility fails for any other reason.
150
152 It is frequently desirable to apply nohup to pipelines or lists of com‐
153 mands. This can be done by placing pipelines and command lists in a
154 single file; this file can then be invoked as a utility, and the nohup
155 applies to everything in the file.
156 Alternatively, the following command can be used to apply nohup to a
158 complex command:
159 nohup sh -c 'complex-command-line' </dev/null
162
164 The 4.3 BSD version ignores SIGTERM and SIGHUP, and if ./nohup.out can‐
165 not be used, it fails instead of trying to use $HOME/nohup.out.
166 The csh utility has a built-in version of nohup that acts differently
168 from the nohup defined in this volume of POSIX.1‐2017.
169 The term utility is used, rather than command, to highlight the fact
171 that shell compound commands, pipelines, special built-ins, and so on,
172 cannot be used directly. However, utility includes user application
173 programs and shell scripts, not just the standard utilities.
174 Historical versions of the nohup utility use default file creation
176 semantics. Some more recent versions use the permissions specified here
177 as an added security precaution.
178 Some historical implementations ignore SIGQUIT in addition to SIGHUP;
180 others ignore SIGTERM. An early proposal allowed, but did not require,
181 SIGQUIT to be ignored. Several reviewers objected that nohup should
182 only modify the handling of SIGHUP as required by this volume of
183 POSIX.1‐2017.
184 Historical versions of nohup did not affect standard input, but that
186 causes problems in the common scenario where the user logs into a sys‐
187 tem, types the command:
188 nohup make &
191 at the prompt, and then logs out. If standard input is not affected by
193 nohup, the login session may not terminate for quite some time, since
194 standard input remains open until make exits. To avoid this problem,
195 POSIX.1‐2008 allows implementations to redirect standard input if it is
196 a terminal. Since the behavior is implementation-defined, portable
197 applications that may run into the problem should redirect standard
198 input themselves. For example, instead of:
199 nohup make &
202 an application can invoke:
204 nohup make </dev/null &
207
209 None.
210
212 Chapter 2, Shell Command Language, sh
213 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
215 Variables
216 The System Interfaces volume of POSIX.1‐2017, signal()
218
220 Portions of this text are reprinted and reproduced in electronic form
221 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
222 table Operating System Interface (POSIX), The Open Group Base Specifi‐
223 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
224 Electrical and Electronics Engineers, Inc and The Open Group. In the
225 event of any discrepancy between this version and the original IEEE and
226 The Open Group Standard, the original IEEE and The Open Group Standard
227 is the referee document. The original Standard can be obtained online
228 at http://www.opengroup.org/unix/online.html .
229 Any typographical or formatting errors that appear in this page are
231 most likely to have been introduced during the conversion of the source
232 files to man page format. To report such errors, see https://www.ker‐
233 nel.org/doc/man-pages/reporting_bugs.html .
234IEEE/The Open Group 2017 NOHUP(1P)