проблема уровня оболочки в ubuntu 20.04
следующая команда получила возвращаемое значение 1 для ubuntu 20.04, но 0 для ubuntu 18.04,
$ ssh user@remote bash -exl -c 'exit 0'
основная причина в том, что у нас разные значения $ SHLVL при запуске команды для разных версий ubuntu, так что это ожидаемое поведение?
+ '[' '' ']'
+ '[' -d /etc/profile.d ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/01-locale-fix.sh ']'
+ . /etc/profile.d/01-locale-fix.sh
+++ /usr/bin/locale-check C.UTF-8
++ eval
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/apps-bin-path.sh ']'
+ . /etc/profile.d/apps-bin-path.sh
++ snap_bin_path=/snap/bin
++ '[' -n /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games -a -n /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games ']'
++ export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
++ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
++ '[' -z '' ']'
++ export XDG_DATA_DIRS=/usr/local/share:/usr/share
++ XDG_DATA_DIRS=/usr/local/share:/usr/share
++ snap_xdg_path=/var/lib/snapd/desktop
++ '[' -n /usr/local/share:/usr/share -a -n /usr/local/share:/usr/share ']'
++ export XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
++ XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/bash_completion.sh ']'
+ . /etc/profile.d/bash_completion.sh
++ '[' 'x5.0.17(1)-release' '!=' x -a x '!=' x -a x = x ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/cedilla-portuguese.sh ']'
+ . /etc/profile.d/cedilla-portuguese.sh
++ '[' en = pt -a en '!=' pt ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/gawk.sh ']'
+ . /etc/profile.d/gawk.sh
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/Z97-byobu.sh ']'
+ . /etc/profile.d/Z97-byobu.sh
++ '[' -r /usr/bin/byobu-launch ']'
++ '[' '' = 0 ']'
++ '[' '' = 1 ']'
++ '[' -e /etc/byobu/autolaunch ']'
++ '[' '' = byobu ']'
++ '[' '' = byobu-screen ']'
++ '[' '' = byobu-tmux ']'
+ unset i
+ '[' -n '5.0.17(1)-release' ']'
+ '[' -f /home/jenkins/.bashrc ']'
+ . /home/jenkins/.bashrc
++ case $- in
++ return
+ '[' -d /home/jenkins/bin ']'
+ PATH=/home/jenkins/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
+ exit
++ '[' 1 = 1 ']'
++ '[' -x /usr/bin/clear_console ']'
++ /usr/bin/clear_console -q
и результат той же команды, запущенной для ubuntu 18.04,
+ '[' '' ']'
+ '[' -d /etc/profile.d ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/01-locale-fix.sh ']'
+ . /etc/profile.d/01-locale-fix.sh
+++ /usr/bin/locale-check C.UTF-8
++ eval
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/apps-bin-path.sh ']'
+ . /etc/profile.d/apps-bin-path.sh
++ snap_bin_path=/snap/bin
++ '[' -n /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games -a -n /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games ']'
++ export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
++ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
++ '[' -z '' ']'
++ export XDG_DATA_DIRS=/usr/local/share:/usr/share
++ XDG_DATA_DIRS=/usr/local/share:/usr/share
++ snap_xdg_path=/var/lib/snapd/desktop
++ '[' -n /usr/local/share:/usr/share -a -n /usr/local/share:/usr/share ']'
++ export XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
++ XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/bash_completion.sh ']'
+ . /etc/profile.d/bash_completion.sh
++ '[' -n '4.4.20(1)-release' -a -n '' -a -z '' ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/cedilla-portuguese.sh ']'
+ . /etc/profile.d/cedilla-portuguese.sh
++ '[' en = pt -a en '!=' pt ']'
+ for i in /etc/profile.d/*.sh
+ '[' -r /etc/profile.d/Z97-byobu.sh ']'
+ . /etc/profile.d/Z97-byobu.sh
++ '[' -r /usr/bin/byobu-launch ']'
++ '[' '' = 0 ']'
++ '[' '' = 1 ']'
++ '[' -e /etc/byobu/autolaunch ']'
++ '[' '' = byobu ']'
++ '[' '' = byobu-screen ']'
++ '[' '' = byobu-tmux ']'
+ unset i
+ '[' -n '4.4.20(1)-release' ']'
+ '[' -f /home/jenkins/.bashrc ']'
+ . /home/jenkins/.bashrc
++ case $- in
++ return
+ '[' -d /home/jenkins/bin ']'
+ PATH=/home/jenkins/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
+ exit
++ '[' 2 = 1 ']'
1 ответ
Looking around, this has been discussed somewhat in the bug-bash mailing lists, where Stéphane Chazelas though it would be due to a fix in the behaviour of SHLVL when bash does tail call optimization.
Essentially, when you do bash -c 'simple-command', bash usually performs an optimization: instead of forking and then execing the simple-command, it directly exec the simple command. This is a common optmization, other shells like zsh also do the same thing. Earlier, in some cases it would be changed incorrectly, and a change was made to fix that, which broke this particular use.
For example, in 18.04's bash 4.4-19, you can see the SHLVL get incremented even though no new process was started:
# env SHLVL=0 strace -fe execve bash -c 'bash -c "declare -p SHLVL"'
execve("/bin/bash", ["bash", "-c", "bash -c \"declare -p SHLVL\""], 0x7ffd6525c6f0 /* 8 vars */) = 0
execve("/bin/bash", ["bash", "-c", "declare -p SHLVL"], 0x562fd3b437e0 /* 8 vars */) = 0
declare -x SHLVL="2"
This would have been the right behaviour with a fork, like when that optimization isn't done:
# env SHLVL=0 strace -fe execve bash -c ':; bash -c "declare -p SHLVL"'
execve("/bin/bash", ["bash", "-c", ":; bash -c \"declare -p SHLVL\""], 0x7ffea8bb7c30 /* 8 vars */) = 0
strace: Process 284 attached
[pid 284] execve("/bin/bash", ["bash", "-c", "declare -p SHLVL"], 0x55fe735077e0 /* 8 vars */) = 0
declare -x SHLVL="2"
[pid 284] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=284, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
+++ exited with 0 +++
This is fixed in bash 5.0, where:
% env SHLVL=0 strace -fe execve bash -c 'bash -c "declare -p SHLVL"'
execve("/usr/bin/bash", ["bash", "-c", "bash -c \"declare -p SHLVL\""], 0x7ffc70b6cd20 /* 59 vars */) = 0
execve("/usr/bin/bash", ["bash", "-c", "declare -p SHLVL"], 0x55f22a0343a0 /* 59 vars */) = 0
declare -x SHLVL="1"
+++ exited with 0 +++
Where this is going wrong, IMO, is in the check in .bash_logout, which I think isn't precise enough. Simply checking for SHLVL isn't enough, if it's going to clear the terminal, it should also check whether it's actually running in a terminal. Something like [ -t 0 ]:
-t FD True if FD is opened on a terminal.
This is, IMHO, a bug in Ubuntu's (well, Debian's) .bash_logout and should be reported as one. SHLVL isn't standard, so I don't think it's good enough to be the sole test when shells can make optimizations that might affect its value.