Linux nohup and exec - Revision history

Pio2pio at 12:01, 5 March 2020

2020-03-05T12:01:31Z

← Older revision		Revision as of 14:01, 5 March 2020
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	<code>nohup</code> and <code>exec</code> commands do different things.		<code>nohup</code> and <code>exec</code> commands do different things.

	*<code>exec</code> replaces the shell with another program. Using <code>exec</code> in a simple background job isn't useful: <code>exec myprogram; more stuff</code> replaces the shell with <code>myprogram</code> and so doesn't run <code>more stuff</code>, unlike <code>myprogram; more stuff</code> which runs more stuff when <code>myprogram</code> terminates; but <code>exec myprogram & more stuff</code> starts <code>myprogram</code> in the background and then runs more stuff, just like <code>myprogram & more stuff</code>.		*<code>exec</code> replaces the shell with another program keeping the same PID. Using <code>exec</code> in a simple background job isn't useful: <code>exec myprogram; more stuff</code> replaces the shell with <code>myprogram</code> and so doesn't run <code>more stuff</code>, unlike <code>myprogram; more stuff</code> which runs more stuff when <code>myprogram</code> terminates; but <code>exec myprogram & more stuff</code> starts <code>myprogram</code> in the background and then runs more stuff, just like <code>myprogram & more stuff</code>.

	*<code>nohup</code> runs the specificed program with the SIGHUP signal ignored. When a terminal is closed, the kernel sends SIGHUP to the controlling process in that terminal (i.e. the shell). The shell in turn sends SIGHUP to all the jobs running in the background. Running a job with <code>nohup</code> prevents it from being killed in this way if the terminal dies (which happens e.g. if you were logged in remotely and the connection drops, or if you close your terminal emulator).		*<code>nohup</code> runs the specificed program with the SIGHUP signal ignored. When a terminal is closed, the kernel sends SIGHUP to the controlling process in that terminal (i.e. the shell). The shell in turn sends SIGHUP to all the jobs running in the background. Running a job with <code>nohup</code> prevents it from being killed in this way if the terminal dies (which happens e.g. if you were logged in remotely and the connection drops, or if you close your terminal emulator).

Pio2pio at 16:54, 6 November 2019

2019-11-06T16:54:22Z

← Older revision		Revision as of 18:54, 6 November 2019
Line 1:		Line 1:
	<code>nohup</code> and <code>exec</code> do different things.		<code>nohup</code> and <code>exec</code> commands do different things.

	*<code>exec</code> replaces the shell with another program. Using <code>exec</code> in a simple background job isn't useful: <code>exec myprogram; more stuff</code> replaces the shell with <code>myprogram</code> and so doesn't run <code>more stuff</code>, unlike <code>myprogram; more stuff</code> which runs more stuff when <code>myprogram</code> terminates; but <code>exec myprogram & more stuff</code> starts <code>myprogram</code> in the background and then runs more stuff, just like <code>myprogram & more stuff</code>.		*<code>exec</code> replaces the shell with another program. Using <code>exec</code> in a simple background job isn't useful: <code>exec myprogram; more stuff</code> replaces the shell with <code>myprogram</code> and so doesn't run <code>more stuff</code>, unlike <code>myprogram; more stuff</code> which runs more stuff when <code>myprogram</code> terminates; but <code>exec myprogram & more stuff</code> starts <code>myprogram</code> in the background and then runs more stuff, just like <code>myprogram & more stuff</code>.
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	</source>		</source>

	~~'''Exec explanation 2'''~~

			;<code>exec</code> command explanation 2
	In example <code>exec firefox</code>, the shell is no longer running: it has been replaced by <code>firefox</code>. You can think of <code>exec</code> as combining exiting a program and starting a new one, but keeping the same process ID. The terminal keeps running because nothing told it to stop. When you later exit Firefox, the firefox process terminates. The terminal notices that its child process has exited and so it exits in turn.		In example <code>exec firefox</code>, the shell is no longer running: it has been replaced by <code>firefox</code>. You can think of <code>exec</code> as combining exiting a program and starting a new one, but keeping the same process ID. The terminal keeps running because nothing told it to stop. When you later exit Firefox, the firefox process terminates. The terminal notices that its child process has exited and so it exits in turn.

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	*<code>nohup </code> - avoids all SIGHUP(terminate signal) and continues execution even if you terminal is closed.		*<code>nohup </code> - avoids all SIGHUP(terminate signal) and continues execution even if you terminal is closed.
	*<code>exec </code> - process dies when a SIGHUP is received, but nohup process continues.		*<code>exec </code> - process dies when a SIGHUP is received, but nohup process continues.


			;<code>nohup</code> command - explanation 2
			<code>nohup</code> is a Unix command that is used to run another command while suppressing the action of the '''HUP (hangup) signal''', enabling the command to keep running after the user who issues the command has logged out. It is most often used to run commands in background as daemons. Output that would normally go to the terminal goes to a file called nohup.out if it has not already been redirected.
			Run a script with nohup command:
			<source lang=bash>
			$ nohup ~/utils/backup "upload" &
			</source>


			The <code>HUP</code> signal is sent to a process when its controlling terminal is closed. It was originally designed to notify the process of a serial line drop (HUP stands for "Hang Up"). In modern systems, this signal usually means that the controlling pseudo or virtual terminal has been closed

	= References =		= References =
	*[https://unix.stackexchange.com/questions/137759/why-use-nohup-rather-than-exec Why use “nohup &” rather than “exec &”] unix.stackexchange.com		*[https://unix.stackexchange.com/questions/137759/why-use-nohup-rather-than-exec Why use “nohup &” rather than “exec &”] unix.stackexchange.com

Pio2pio: Created page with "`nohup` and `exec` do different things. *`exec` replaces the shell with another program. Using `exec` in a simple background job..."

2018-06-09T11:40:36Z

Created page with "<code>nohup</code> and <code>exec</code> do different things. *<code>exec</code> replaces the shell with another program. Using <code>exec</code> in a simple background job..."

New page

<code>nohup</code> and <code>exec</code> do different things.

*<code>exec</code> replaces the shell with another program. Using <code>exec</code> in a simple background job isn't useful: <code>exec myprogram; more stuff</code> replaces the shell with <code>myprogram</code> and so doesn't run <code>more stuff</code>, unlike <code>myprogram; more stuff</code> which runs more stuff when <code>myprogram</code> terminates; but <code>exec myprogram & more stuff</code> starts <code>myprogram</code> in the background and then runs more stuff, just like <code>myprogram & more stuff</code>.

*<code>nohup</code> runs the specificed program with the SIGHUP signal ignored. When a terminal is closed, the kernel sends SIGHUP to the controlling process in that terminal (i.e. the shell). The shell in turn sends SIGHUP to all the jobs running in the background. Running a job with <code>nohup</code> prevents it from being killed in this way if the terminal dies (which happens e.g. if you were logged in remotely and the connection drops, or if you close your terminal emulator).

*<code>nohup</code> also redirects the program's output to the file <code>nohup.out</code>. This avoids the program dying because it isn't able to write to its output or error output. Note that nohup doesn't redirect the input. To fully disconnect a program from the terminal where you launched it, use

<source lang="bash">
nohup myprogram </dev/null >myprogram.log 2>&1 &
</source>

'''Exec explanation 2'''

In example <code>exec firefox</code>, the shell is no longer running: it has been replaced by <code>firefox</code>. You can think of <code>exec</code> as combining exiting a program and starting a new one, but keeping the same process ID. The terminal keeps running because nothing told it to stop. When you later exit Firefox, the firefox process terminates. The terminal notices that its child process has exited and so it exits in turn.

*<code>exec & </code> - executes a process as a background process so you may continue using the same terminal for other jobs.
*<code>nohup </code> - avoids all SIGHUP(terminate signal) and continues execution even if you terminal is closed.
*<code>exec </code> - process dies when a SIGHUP is received, but nohup process continues.

= References =
*[https://unix.stackexchange.com/questions/137759/why-use-nohup-rather-than-exec Why use “nohup &” rather than “exec &”] unix.stackexchange.com

Linux nohup and exec - Revision history

Pio2pio at 12:01, 5 March 2020

Pio2pio at 16:54, 6 November 2019

Pio2pio: Created page with "nohup and exec do different things. *exec replaces the shell with another program. Using exec in a simple background job..."

Pio2pio: Created page with "`nohup` and `exec` do different things. *`exec` replaces the shell with another program. Using `exec` in a simple background job..."