Why do some programs' processes exist after forking a child, without the child starting a new process...
Here are some of the steps for creating a daemon process from a given process,
the given process exists soon after forking a child,
the child calls start a new session and also a new group, by
setsid()
But I seem to find cases with only the first step without the second step:
in a login session under a desktop environment
in an interactive bash process.
What is the purpose of only having the first step without the second step?
Does it not want to create a daemon but something else?
Thanks.
linux bash process session
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
add a comment |
Here are some of the steps for creating a daemon process from a given process,
the given process exists soon after forking a child,
the child calls start a new session and also a new group, by
setsid()
But I seem to find cases with only the first step without the second step:
in a login session under a desktop environment
in an interactive bash process.
What is the purpose of only having the first step without the second step?
Does it not want to create a daemon but something else?
Thanks.
linux bash process session
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
add a comment |
Here are some of the steps for creating a daemon process from a given process,
the given process exists soon after forking a child,
the child calls start a new session and also a new group, by
setsid()
But I seem to find cases with only the first step without the second step:
in a login session under a desktop environment
in an interactive bash process.
What is the purpose of only having the first step without the second step?
Does it not want to create a daemon but something else?
Thanks.
linux bash process session
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
Here are some of the steps for creating a daemon process from a given process,
the given process exists soon after forking a child,
the child calls start a new session and also a new group, by
setsid()
But I seem to find cases with only the first step without the second step:
in a login session under a desktop environment
in an interactive bash process.
What is the purpose of only having the first step without the second step?
Does it not want to create a daemon but something else?
Thanks.
linux bash process session
linux bash process session
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
edited Dec 27 '18 at 22:10
Tim
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
asked Dec 27 '18 at 17:46
TimTim
26.3k74246455
26.3k74246455
add a comment |
add a comment |
1 Answer
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The purpose, on high level, is best seen in the bash example that you gave. When, in an interactive bash shell, a normal user types ls, what happens is
- Bash forks
- the child process execs
ls
- when
lsis finished, the child process ends
It would be silly to daemonize ls, because (in general) it ends very quickly.
Furthermore, it would also be strange is all processes that are forked from a shell would do a setuid(). You would then not be able to run a shell as a normal user.
Do not take the specifics of daemons as the general rule for the use of fork/exec.
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changedsetuid()in your question tosetsid(), which makes my remark aboutsetuid()no longer applicable.
– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The purpose, on high level, is best seen in the bash example that you gave. When, in an interactive bash shell, a normal user types ls, what happens is
- Bash forks
- the child process execs
ls
- when
lsis finished, the child process ends
It would be silly to daemonize ls, because (in general) it ends very quickly.
Furthermore, it would also be strange is all processes that are forked from a shell would do a setuid(). You would then not be able to run a shell as a normal user.
Do not take the specifics of daemons as the general rule for the use of fork/exec.
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changedsetuid()in your question tosetsid(), which makes my remark aboutsetuid()no longer applicable.
– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
add a comment |
The purpose, on high level, is best seen in the bash example that you gave. When, in an interactive bash shell, a normal user types ls, what happens is
- Bash forks
- the child process execs
ls
- when
lsis finished, the child process ends
It would be silly to daemonize ls, because (in general) it ends very quickly.
Furthermore, it would also be strange is all processes that are forked from a shell would do a setuid(). You would then not be able to run a shell as a normal user.
Do not take the specifics of daemons as the general rule for the use of fork/exec.
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changedsetuid()in your question tosetsid(), which makes my remark aboutsetuid()no longer applicable.
– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
add a comment |
The purpose, on high level, is best seen in the bash example that you gave. When, in an interactive bash shell, a normal user types ls, what happens is
- Bash forks
- the child process execs
ls
- when
lsis finished, the child process ends
It would be silly to daemonize ls, because (in general) it ends very quickly.
Furthermore, it would also be strange is all processes that are forked from a shell would do a setuid(). You would then not be able to run a shell as a normal user.
Do not take the specifics of daemons as the general rule for the use of fork/exec.
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
The purpose, on high level, is best seen in the bash example that you gave. When, in an interactive bash shell, a normal user types ls, what happens is
- Bash forks
- the child process execs
ls
- when
lsis finished, the child process ends
It would be silly to daemonize ls, because (in general) it ends very quickly.
Furthermore, it would also be strange is all processes that are forked from a shell would do a setuid(). You would then not be able to run a shell as a normal user.
Do not take the specifics of daemons as the general rule for the use of fork/exec.
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
edited Dec 27 '18 at 19:04
Tim
26.3k74246455
26.3k74246455
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
answered Dec 27 '18 at 18:51
Ljm DullaartLjm Dullaart
58817
58817
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changedsetuid()in your question tosetsid(), which makes my remark aboutsetuid()no longer applicable.
– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
add a comment |
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changedsetuid()in your question tosetsid(), which makes my remark aboutsetuid()no longer applicable.
– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
Thanks, I didn't ask how a shell executes an external command in general.
– Tim
Dec 27 '18 at 22:09
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
The point is in the last sentence: you seem to take the process of daemonisation as the norm.
– Ljm Dullaart
Dec 27 '18 at 23:18
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
I didn't. Please reread my post.
– Tim
Dec 29 '18 at 2:49
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changed
setuid() in your question to setsid(), which makes my remark about setuid() no longer applicable.– Ljm Dullaart
Dec 29 '18 at 13:26
"Does it not want to create a daemon but something else?" The answer then is "something else". I also noticed that you changed
setuid() in your question to setsid(), which makes my remark about setuid() no longer applicable.– Ljm Dullaart
Dec 29 '18 at 13:26
That's my typo.
– Tim
Dec 29 '18 at 13:28
That's my typo.
– Tim
Dec 29 '18 at 13:28
add a comment |
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