What happens to a unix session when the session leader exits?
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I'm trying to properly emulate POSIX signals handling and job control for my pet operating system, but it's not clear to me what should happen to a session after the session leader exits.
I cannot find documentation related to what happens to the session and its process if, for example, a child kills the session leader while several background processes and a different foreground process are running.
My tests show that all the process in the session are killed, but how?
Do they receive a specific signal?
Is this case specified in the POSIX standard? And if so, can you provide some references?
posix process-management
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
add a comment |Â
up vote
1
down vote
favorite
I'm trying to properly emulate POSIX signals handling and job control for my pet operating system, but it's not clear to me what should happen to a session after the session leader exits.
I cannot find documentation related to what happens to the session and its process if, for example, a child kills the session leader while several background processes and a different foreground process are running.
My tests show that all the process in the session are killed, but how?
Do they receive a specific signal?
Is this case specified in the POSIX standard? And if so, can you provide some references?
posix process-management
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I'm trying to properly emulate POSIX signals handling and job control for my pet operating system, but it's not clear to me what should happen to a session after the session leader exits.
I cannot find documentation related to what happens to the session and its process if, for example, a child kills the session leader while several background processes and a different foreground process are running.
My tests show that all the process in the session are killed, but how?
Do they receive a specific signal?
Is this case specified in the POSIX standard? And if so, can you provide some references?
posix process-management
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
I'm trying to properly emulate POSIX signals handling and job control for my pet operating system, but it's not clear to me what should happen to a session after the session leader exits.
I cannot find documentation related to what happens to the session and its process if, for example, a child kills the session leader while several background processes and a different foreground process are running.
My tests show that all the process in the session are killed, but how?
Do they receive a specific signal?
Is this case specified in the POSIX standard? And if so, can you provide some references?
posix process-management
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
asked Nov 28 '17 at 9:35
Giacomo Tesio
4551615
4551615
Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52
add a comment |Â
Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52
Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
3
down vote
accepted
You are not the only one puzzled by POSIX sessions; Lennart Poettering (he of systemd fame) is puzzled too.
As far as anybody can tell, when a session leader dies, init inherits the orphaned session and
All session member processes in the foreground process group (if any) receive a SIGHUP.
Session member processes who are not in the foreground group don't receive any signal.
See also:
- notes.shichao.io/apue/ch9
- Chapter 10 "Processes" in The Linux Kernel by Andries Brouwer (2003).
If the terminal goes away by modem hangup, and the line was not local, then a SIGHUP is sent to the session leader. [...] When the session leader dies, a SIGHUP is sent to all processes in the foreground process group. [...] Thus, if the terminal goes away and the session leader is a job control shell, then it can handle things for its descendants, e.g. by sending them again a SIGHUP. If on the other hand the session leader is an innocent process that does not catch SIGHUP, it will die, and all foreground processes get a SIGHUP.
Andries Brower, The Linux Kernel, section 10.3 "Sessions".
answered Nov 28 '17 at 11:28
AlexP
6,656924
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
You are not the only one puzzled by POSIX sessions; Lennart Poettering (he of systemd fame) is puzzled too.
As far as anybody can tell, when a session leader dies, init inherits the orphaned session and
All session member processes in the foreground process group (if any) receive a SIGHUP.
Session member processes who are not in the foreground group don't receive any signal.
See also:
- notes.shichao.io/apue/ch9
- Chapter 10 "Processes" in The Linux Kernel by Andries Brouwer (2003).
If the terminal goes away by modem hangup, and the line was not local, then a SIGHUP is sent to the session leader. [...] When the session leader dies, a SIGHUP is sent to all processes in the foreground process group. [...] Thus, if the terminal goes away and the session leader is a job control shell, then it can handle things for its descendants, e.g. by sending them again a SIGHUP. If on the other hand the session leader is an innocent process that does not catch SIGHUP, it will die, and all foreground processes get a SIGHUP.
Andries Brower, The Linux Kernel, section 10.3 "Sessions".
answered Nov 28 '17 at 11:28
AlexP
6,656924
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
add a comment |Â
up vote
3
down vote
accepted
You are not the only one puzzled by POSIX sessions; Lennart Poettering (he of systemd fame) is puzzled too.
As far as anybody can tell, when a session leader dies, init inherits the orphaned session and
All session member processes in the foreground process group (if any) receive a SIGHUP.
Session member processes who are not in the foreground group don't receive any signal.
See also:
- notes.shichao.io/apue/ch9
- Chapter 10 "Processes" in The Linux Kernel by Andries Brouwer (2003).
If the terminal goes away by modem hangup, and the line was not local, then a SIGHUP is sent to the session leader. [...] When the session leader dies, a SIGHUP is sent to all processes in the foreground process group. [...] Thus, if the terminal goes away and the session leader is a job control shell, then it can handle things for its descendants, e.g. by sending them again a SIGHUP. If on the other hand the session leader is an innocent process that does not catch SIGHUP, it will die, and all foreground processes get a SIGHUP.
Andries Brower, The Linux Kernel, section 10.3 "Sessions".
answered Nov 28 '17 at 11:28
AlexP
6,656924
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
add a comment |Â
up vote
3
down vote
accepted
up vote
3
down vote
accepted
You are not the only one puzzled by POSIX sessions; Lennart Poettering (he of systemd fame) is puzzled too.
As far as anybody can tell, when a session leader dies, init inherits the orphaned session and
All session member processes in the foreground process group (if any) receive a SIGHUP.
Session member processes who are not in the foreground group don't receive any signal.
See also:
- notes.shichao.io/apue/ch9
- Chapter 10 "Processes" in The Linux Kernel by Andries Brouwer (2003).
If the terminal goes away by modem hangup, and the line was not local, then a SIGHUP is sent to the session leader. [...] When the session leader dies, a SIGHUP is sent to all processes in the foreground process group. [...] Thus, if the terminal goes away and the session leader is a job control shell, then it can handle things for its descendants, e.g. by sending them again a SIGHUP. If on the other hand the session leader is an innocent process that does not catch SIGHUP, it will die, and all foreground processes get a SIGHUP.
Andries Brower, The Linux Kernel, section 10.3 "Sessions".
answered Nov 28 '17 at 11:28
AlexP
6,656924
You are not the only one puzzled by POSIX sessions; Lennart Poettering (he of systemd fame) is puzzled too.
As far as anybody can tell, when a session leader dies, init inherits the orphaned session and
All session member processes in the foreground process group (if any) receive a SIGHUP.
Session member processes who are not in the foreground group don't receive any signal.
See also:
- notes.shichao.io/apue/ch9
- Chapter 10 "Processes" in The Linux Kernel by Andries Brouwer (2003).
If the terminal goes away by modem hangup, and the line was not local, then a SIGHUP is sent to the session leader. [...] When the session leader dies, a SIGHUP is sent to all processes in the foreground process group. [...] Thus, if the terminal goes away and the session leader is a job control shell, then it can handle things for its descendants, e.g. by sending them again a SIGHUP. If on the other hand the session leader is an innocent process that does not catch SIGHUP, it will die, and all foreground processes get a SIGHUP.
Andries Brower, The Linux Kernel, section 10.3 "Sessions".
answered Nov 28 '17 at 11:28
AlexP
6,656924
edited Nov 28 '17 at 16:12
answered Nov 28 '17 at 11:28
AlexP
6,656924
answered Nov 28 '17 at 11:28
AlexP
6,656924
answered Nov 28 '17 at 11:28
AlexP
6,656924
6,656924
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
add a comment |Â
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
As for "All session member processes in the foreground process group (if any) receive a SIGHUP.": do you know who send the SIGHUP? In unix.stackexchange.com/questions/84737/… it seems that bash send the signal... and this would invalidate part of your answer.
– Giacomo Tesio
Nov 28 '17 at 14:37
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
@GiacomoTesio: See added quotation from The Linux Kernel.
– AlexP
Nov 28 '17 at 16:09
add a comment |Â
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Some related questions are unix.stackexchange.com/questions/405755 , unix.stackexchange.com/questions/84737 , unix.stackexchange.com/questions/18166 , and unix.stackexchange.com/questions/282973 .
– JdeBP
Nov 28 '17 at 10:16
@JdeBP interesting links, but it's still hard to say what is expected to happen if the session leader exits. Even considered that the session leader might not be a shell.
– Giacomo Tesio
Nov 28 '17 at 10:52