千言万语，不如实验来的直接...

基于sleep的小实验

首先通过实验直观感受一下后台服务的运行状况（请注意，前方高能，相关概念在更后面才有解释）。

在命令行上以不同方式执行 sleep

确定登录 shell 和伪终端。

[root@YOYO ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

0 1 1 1 ? -1 Ss 0 0:02 /sbin/init

...

1 1654 1654 1654 ? -1 Ss 0 0:00 /usr/sbin/sshd

1654 15437 15437 15437 ? -1 Ss 0 0:00 \_ sshd: root@pts/0,pts/1

15437 15441 15441 15441 pts/0 15441 Ss+ 0 0:00 \_ -bash

15437 16237 16237 16237 pts/1 16258 Ss 0 0:00 \_ -bash

16237 16258 16258 16237 pts/1 16258 R+ 0 0:00 \_ ps ajxf

...

[root@YOYO ~]#

分别以后台方式（&）、setsid、nohup 和前台方式执行 sleep

[root@YOYO ~]# jobs -l

[root@YOYO ~]#

[root@YOYO ~]# sleep 600 & -- 通过 & 后台运行 -- 1

[1] 16261

[root@YOYO ~]#

[root@YOYO ~]# setsid sleep 660 -- 通过 setsid 后台运行 -- 2

[root@YOYO ~]#

[root@YOYO ~]# nohup sleep 720 & -- 通过 nohup + & 后台运行 -- 3

[2] 16271

[root@YOYO ~]# nohup: 忽略输入并把输出追加到"nohup.out"

[root@YOYO ~]#

[root@YOYO ~]# sleep 780 -- 前台运行 -- 4

^Z -- 挂起

[3]+ Stopped sleep 780

[root@YOYO ~]#

[root@YOYO ~]# jobs -l

[1] 16261 Running sleep 600 &

[2]- 16271 Running nohup sleep 720 &

[3]+ 16274 停止 sleep 780

[root@YOYO ~]#

[root@YOYO ~]# bg 3 -- 放入后台运行

[3]+ sleep 780 &

[root@YOYO ~]#

[root@YOYO ~]# jobs -l

[1] 16261 Running sleep 600 &

[2]- 16271 Running nohup sleep 720 &

[3]+ 16274 Running sleep 780 &

[root@YOYO ~]#

查看此时的进程关系

[root@YOYO ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

0 1 1 1 ? -1 Ss 0 0:02 /sbin/init

...

1 1654 1654 1654 ? -1 Ss 0 0:00 /usr/sbin/sshd

1654 15437 15437 15437 ? -1 Ss 0 0:00 \_ sshd: root@pts/0,pts/1

15437 15441 15441 15441 pts/0 15441 Ss+ 0 0:00 \_ -bash

15437 16237 16237 16237 pts/1 16282 Ss 0 0:00 \_ -bash

16237 16261 16261 16237 pts/1 16282 S 0 0:00 \_ sleep 600 -- 1

16237 16271 16271 16237 pts/1 16282 S 0 0:00 \_ sleep 720 -- 3

16237 16274 16274 16237 pts/1 16282 S 0 0:00 \_ sleep 780 -- 4

16237 16282 16282 16237 pts/1 16282 R+ 0 0:00 \_ ps ajxf

...

1 16265 16265 16265 ? -1 Ss 0 0:00 sleep 660 -- 2

[root@YOYO ~]#

叉掉 ssh 连接窗口，查看此时的 sleep 进程状态

[root@YOYO ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

0 1 1 1 ? -1 Ss 0 0:02 /sbin/init

...

1 1654 1654 1654 ? -1 Ss 0 0:00 /usr/sbin/sshd

1654 15437 15437 15437 ? -1 Ss 0 0:00 \_ sshd: root@pts/0

15437 15441 15441 15441 pts/0 16300 Ss 0 0:00 \_ -bash

15441 16300 16300 15441 pts/0 16300 R+ 0 0:00 \_ ps ajxf

...

1 16265 16265 16265 ? -1 Ss 0 0:00 sleep 660 -- 2

1 16271 16271 16237 ? -1 S 0 0:00 sleep 720 -- 3

[root@YOYO ~]#

实验结论：
以不同方式启动进程，在 ssh 连接窗口被叉掉的时候会造成不同的影响。标号为 1 和 4 的两个进程都消失了，标号为 3 的进程有属性发生了变化，只有标号为 2 的进程没有任何改变。

在 shell 脚本中上以不同方式执行 sleep

测试一（前台进程组）

[root@Betty ~]# vi test_1.sh

#!/bin/sh

sleep 600 # 会卡住当前 shell 脚本

[root@Betty ~]#

[root@Betty ~]# ./test_1.sh

（卡住）

在另一个窗口中查看

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1,pts/2

13331 16993 16993 16993 pts/1 18649 Ss 0 0:00 \_ -bash

16993 18649 18649 16993 pts/1 18649 R+ 0 0:00 | \_ ps ajxf

13331 18572 18572 18572 pts/2 18632 Ss 0 0:00 \_ -bash

18572 18632 18632 18572 pts/2 18632 S+ 0 0:00 \_ /bin/sh ./test_1.sh

18632 18633 18632 18572 pts/2 18632 S+ 0 0:00 \_ sleep 600

此时叉掉启动 test_1.sh 脚本的窗口，可以看到对应的进程全部消失。

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1

13331 16993 16993 16993 pts/1 18706 Ss 0 0:00 \_ -bash

16993 18706 18706 16993 pts/1 18706 R+ 0 0:00 \_ ps ajxf

测试二（孤儿后台进程组）

[root@Betty ~]# vi test_2.sh

#!/bin/sh

sleep 600 & # 不会卡住当前 shell 脚本，因为放在后台执行

[root@Betty ~]#

[root@Betty ~]# ./test_2.sh

[root@Betty ~]#

在另一个窗口中查看

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1,pts/0

13331 16993 16993 16993 pts/1 18778 Ss 0 0:00 \_ -bash

16993 18778 18778 16993 pts/1 18778 R+ 0 0:00 | \_ ps ajxf

13331 18734 18734 18734 pts/0 18734 Ss+ 0 0:00 \_ -bash

...

1 18763 18762 18734 pts/0 18734 S 0 0:00 sleep 600 -- 对应后台执行 sleep 的进程，由于是后台执行，

所以不会卡住 test.sh 脚本的执行

test.sh 脚本执行结束后，与 test.sh 对应的进程

会自行退出，从而 sleep 进程被 init 进程收养

此时叉掉启动 test_2.sh 脚本的窗口，可以看到 sleep 600 对应进程的 TTY 和 TPGID 发生了变化，但进程并未消失。

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1

13331 16993 16993 16993 pts/1 18816 Ss 0 0:00 \_ -bash

16993 18816 18816 16993 pts/1 18816 R+ 0 0:00 \_ ps ajxf

...

1 18763 18762 18734 ? -1 S 0 0:00 sleep 600

测试三（前台进程组）

[root@Betty ~]# vi test_3.sh

#!/bin/sh

sleep 600 &

sleep 720

[root@Betty ~]#

[root@Betty ~]# ./test_3.sh

（卡住）

在另一个窗口中查看

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1,pts/2

13331 16993 16993 16993 pts/1 18918 Ss 0 0:00 \_ -bash

16993 18918 18918 16993 pts/1 18918 R+ 0 0:00 | \_ ps ajxf

13331 18856 18856 18856 pts/2 18908 Ss 0 0:00 \_ -bash

18856 18908 18908 18856 pts/2 18908 S+ 0 0:00 \_ /bin/sh ./test_3.sh

18908 18909 18908 18856 pts/2 18908 S+ 0 0:00 \_ sleep 600

18908 18910 18908 18856 pts/2 18908 S+ 0 0:00 \_ sleep 720

...

[root@Betty ~]#

此时叉掉启动 test_3.sh 脚本的窗口，可以看到对应的进程全部消失。

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1

13331 16993 16993 16993 pts/1 18963 Ss 0 0:00 \_ -bash

16993 18963 18963 16993 pts/1 18963 R+ 0 0:00 \_ ps ajxf

...

[root@Betty ~]#

测试四（后台进程组）

[root@Betty ~]# cat test_1.sh

#!/bin/sh

sleep 600

[root@Betty ~]#

[root@Betty ~]# ./test_1.sh & -- 后台执行该脚本

[1] 19016

[root@Betty ~]#

在另外一个窗口中查看

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1,pts/0

13331 16993 16993 16993 pts/1 19032 Ss 0 0:00 \_ -bash

16993 19032 19032 16993 pts/1 19032 R+ 0 0:00 | \_ ps ajxf

13331 18993 18993 18993 pts/0 18993 Ss+ 0 0:00 \_ -bash

18993 19016 19016 18993 pts/0 18993 S 0 0:00 \_ /bin/sh ./test_1.sh

19016 19017 19016 18993 pts/0 18993 S 0 0:00 \_ sleep 600

...

[root@Betty ~]#

此时叉掉后台启动 test_1.sh 脚本的窗口，可以看到对应的进程全部消失。

[root@Betty ~]# ps ajxf

PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND

...

1 1860 1860 1860 ? -1 Ss 0 0:00 /usr/sbin/sshd

1860 13331 13331 13331 ? -1 Ss 0 0:00 \_ sshd: root@pts/1

13331 16993 16993 16993 pts/1 19052 Ss 0 0:00 \_ -bash

16993 19052 19052 16993 pts/1 19052 R+ 0 0:00 \_ ps ajxf

...

[root@Betty ~]#

实验结论：

如果 shell 脚本中存在前台执行的命令，则在其未执行结束前，会“卡住”当前 shell 脚本对应的进程，进而“卡住”bash 进程。即整个进程树在 ps ajxf 中都会作为前台进程组显示。
& 的使用在 shell 脚本内外会产生不同的效果，在 shell 脚本内可以产生孤儿进程组（前提是没有其他命令的执行导致 shell 脚本无法退出），在脚本外则产生普通的后台进程组；
对于孤儿进程组和普通后台进程组 SIGHUP 信号在处理细节上是不同的；

进程消失的原因--SIGHUP

之前整理了一篇关于 SIGHUP 信号的博文，下面给出一些结论：

系统对 SIGHUP 信号的默认处理是终止收到该信号的进程。所以若程序中没有捕捉该信号，当收到该信号时，进程就会退出；
终端（或伪终端）被关闭时，信号 SIGHUP 会被内核发送到具有控制终端的会话的会话首进程；
会话首进程退出前，信号 SIGHUP 会被内核发送到当前会话中的前台进程组中的每一个进程；
bash 收到 SIGHUP 时，会给其下运行的各个作业（包括前后台）发送 SIGHUP，然后自己退出；
前后台的各个作业收到来自 bash 的 SIGHUP 后将退出（如果存在针对 SIGHUP 的处理，就不会退出）

基于strace研究各种运行方式的差别

既然知道了进程消失是因为 SIGHUP 信号导致，那么就可以通过 strace 观察各种运行方式下，都做了哪些相关处理。

跟踪前台运行，可以看到其中没有针对 SIGHUP 信号做任何处理。

[root@YOYO ~]# strace sleep 10

execve("/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0xafa000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe54ec09000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fe54ebf7000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe54ebf6000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe54ebf5000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe54ebf4000

arch_prctl(ARCH_SET_FS, 0x7fe54ebf5700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7fe54ebf7000, 70566) = 0

brk(0) = 0xafa000

brk(0xb1b000) = 0xb1b000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fe548d64000

close(3) = 0

nanosleep({10, 0}, NULL) = 0 -- 对应 sleep 10

close(1) = 0

close(2) = 0

exit_group(0) = ?

[root@YOYO ~]#

跟踪后台运行，可以看到其中同样没有针对SIGHUP信号做任何处理。

[root@YOYO ~]# strace sleep 10 &

[1] 2727

[root@YOYO ~]# execve("/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0x1406000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ff18790f000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7ff1878fd000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ff1878fc000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ff1878fb000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ff1878fa000

arch_prctl(ARCH_SET_FS, 0x7ff1878fb700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7ff1878fd000, 70566) = 0

brk(0) = 0x1406000

brk(0x1427000) = 0x1427000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7ff181a6a000

close(3) = 0

nanosleep({10, 0}, NULL) = 0 -- 对应 sleep 10

close(1) = 0

close(2) = 0

exit_group(0) = ?

[1]+ Done strace sleep 10

[root@YOYO ~]#

跟踪 setsid 的使用，可以看到其中同样没有针对 SIGHUP 信号做任何处理（通过 setsid 执行后不会退出的原因后续再说明）。

[root@YOYO ~]# strace setsid sleep 10

execve("/usr/bin/setsid", ["setsid", "sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0x1274000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2dc78d4000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2dc78c2000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2dc78c1000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2dc78c0000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2dc78bf000

arch_prctl(ARCH_SET_FS, 0x7f2dc78c0700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7f2dc78c2000, 70566) = 0

brk(0) = 0x1274000

brk(0x1295000) = 0x1295000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2dc1a2f000

close(3) = 0

getpgrp() = 2743 -- 获取进程组 id

getpid() = 2744 -- 获取进程 id

setsid() = 2744 -- 创建新的会话

execve("/usr/lib64/qt-3.3/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/usr/local/sbin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/usr/local/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/sbin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0x1f96000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f60207fc000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f60207ea000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f60207e9000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f60207e8000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f60207e7000

arch_prctl(ARCH_SET_FS, 0x7f60207e8700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7f60207ea000, 70566) = 0

brk(0) = 0x1f96000

brk(0x1fb7000) = 0x1fb7000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f601a957000

close(3) = 0

nanosleep({10, 0}, NULL) = 0 -- 对应 sleep 10

close(1) = 0

close(2) = 0

exit_group(0) = ?

[root@YOYO ~]#

跟踪 nohup 的使用，可以看到内部设置了对 SIGHUP 信号的忽略处理。

100

101

102

103

104

105

106

107

108

109

[root@YOYO ~]# strace nohup sleep 10 &

[1] 763

[root@YOYO ~]# execve("/usr/bin/nohup", ["nohup", "sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0x138b000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f41c123d000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f41c122b000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f41c122a000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f41c1229000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f41c1228000

arch_prctl(ARCH_SET_FS, 0x7f41c1229700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7f41c122b000, 70566) = 0

brk(0) = 0x138b000

brk(0x13ac000) = 0x13ac000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f41bb398000

close(3) = 0

ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig -icanon -echo ...}) = 0

ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig -icanon -echo ...}) = 0

ioctl(2, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig -icanon -echo ...}) = 0

open("/dev/null", O_WRONLY) = 3 -- 以“只写”权限打开 /dev/null

dup2(3, 0) = 0 -- 将标准输入重定向到 /dev/null

close(3) = 0

umask(037777777177) = 022

open("nohup.out", O_WRONLY|O_CREAT|O_APPEND, 0600) = 3 -- 打开 nohup.out 文件

dup2(3, 1) = 1 -- 将标准输出重定向到 nohup.out

close(3) = 0

umask(022) = 0177

open("/usr/share/locale/locale.alias", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=2512, ...}) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f41c123c000

read(3, "# Locale name alias data base.\n#"..., 4096) = 2512

read(3, "", 4096) = 0

close(3) = 0

munmap(0x7f41c123c000, 4096) = 0

open("/usr/share/locale/zh_CN.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/usr/share/locale/zh_CN.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/usr/share/locale/zh_CN/LC_MESSAGES/coreutils.mo", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=286636, ...}) = 0

mmap(NULL, 286636, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f41bb352000

close(3) = 0

open("/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=26060, ...}) = 0

mmap(NULL, 26060, PROT_READ, MAP_SHARED, 3, 0) = 0x7f41bb34b000

close(3) = 0

write(2, "nohup: ", 7nohup: ) = 7

write(2, "\345\277\275\347\225\245\350\276\223\345\205\245\345\271\266\346\212\212\350\276\223\345\207\272\350\277\275\345\212\240\345\210"..., 44忽略输入并把输出追加到"nohup.out") = 44

write(2, "\n", 1

) = 1

fcntl(2, F_DUPFD, 3) = 3

fcntl(3, F_GETFD) = 0

fcntl(3, F_SETFD, FD_CLOEXEC) = 0

dup2(1, 2) = 2 -- 将标准出错重定向到 nohuo.out

rt_sigaction(SIGHUP, {SIG_IGN, [HUP], SA_RESTORER|SA_RESTART, 0x3f380326a0}, {SIG_DFL, [], 0}, 8) = 0 -- 设置 SIGHUP 信号处理函数为 SIG_IGN

execve("/usr/lib64/qt-3.3/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/usr/local/sbin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/usr/local/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/sbin/sleep", ["sleep", "10"], [/* 28 vars */]) = -1 ENOENT (No such file or directory)

execve("/bin/sleep", ["sleep", "10"], [/* 28 vars */]) = 0

brk(0) = 0x86a000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc801ecc000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=70566, ...}) = 0

mmap(NULL, 70566, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc801eba000

close(3) = 0

open("/lib64/libc.so.6", O_RDONLY) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0018?\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0

mmap(0x3f38000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3f38000000

mprotect(0x3f3818a000, 2097152, PROT_NONE) = 0

mmap(0x3f3838a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3f3838a000

mmap(0x3f3838f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3f3838f000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc801eb9000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc801eb8000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc801eb7000

arch_prctl(ARCH_SET_FS, 0x7fc801eb8700) = 0

mprotect(0x3f3838a000, 16384, PROT_READ) = 0

mprotect(0x3f37a1f000, 4096, PROT_READ) = 0

munmap(0x7fc801eba000, 70566) = 0

brk(0) = 0x86a000

brk(0x88b000) = 0x88b000

open("/usr/lib/locale/locale-archive", O_RDONLY) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=99154480, ...}) = 0

mmap(NULL, 99154480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc7fc027000

close(3) = 0

nanosleep({10, 0}, NULL) = 0 -- 对应 sleep 10

close(1) = 0

close(2) = 0

exit_group(0) = ?

[1]+ Done strace nohup sleep 10

[root@YOYO ~]#

setsid 和 nohup 的源码实现

通过上面的 strace 输出没有看出，为何通过 setsid 方式启动的程序不会因为 SIGHUP 信号退出的原因（但从理论上讲，我们知道是因为创建的进程没有控制终端的缘故）。下面看一下这两命令的源码实现。

下面是 setsid 的核心源码（取自 util-linux-2.26）

下面给出 nohup 的核心源码（取自 coreutils-8.24）

可以看到，源码实现中的逻辑与 strace 看到的内容完全对应上了。

部署工具脚本中的问题

基于以上的内容，就可以很容易发现或解释我们实际使用中的脚本存在哪些问题（公司内容，略）。

时间： 2024-09-30 15:20:41

【原创】Linux 下程序后台运行相关问题总结

基于sleep的小实验

在命令行上以不同方式执行 sleep

在 shell 脚本中上以不同方式执行 sleep

相关概念

进程消失的原因--SIGHUP

基于strace研究各种运行方式的差别

setsid 和 nohup 的源码实现

部署工具脚本中的问题

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