Arch Linux

Description:

When running mkosi (https://github.com/systemd/mkosi.git) which in turns runs pacstrap when bootstrapping an Arch Linux image, interrupting mkosi (Ctrl+C) during the pacman installation phase makes mkosi's cleanup phase fail as it's unable to unmount <root>/var/cache/pacman/pkg. The umount operation fails with "OSError: [Errno 16] Device or resource busy: 'pkg'". We also see some more output from pacman after the subprocess.run(pacstrap) call in python has already finished.

The problem seems to be that pacman is still running after the pacstrap script exits. pacman correctly receives the SIGINT signal (which we can see from the interrupted message in the output) but unshare doesn't seem to wait until it exits. I tried adding a few 'wait' calls in pacstrap but that doesn't fix the problem. Removing the --fork option from the pacstrap call does fix the problem.

I checked the util-linux source code and unshare doesn't seem to handle the SIGINT and SIGTERM signals. It simply exits when it receives either one without waiting for the child to exit. I made an issue in the util-linux issue tracker as well but maybe we can check if we need the unshare call in pacstrap. It was added in e1a84d105699969a41136ddc0b3f7816ae907bfc but there's no motivation as to why it is necessary. At least for the mkosi use case, everything seems to work fine without it.

Output:

( 91/112) installing device-mapper [############################################################################] 100%
( 92/112) installing popt [############################################################################] 100%
( 93/112) installing json-c [############################################################################] 100%
( 94/112) installing argon2 [############################################################################] 100%
( 95/112) installing cryptsetup [############################################################################] 100%
( 96/112) installing dbus [############################################################################] 100%
( 97/112) installing libmnl [############################################################################] 100%
( 98/112) installing libnftnl [############################################################################] 100%
( 99/112) installing libnl [############################################################################] 100%
(100/112) installing libusb [############################################################################] 100%
(101/112) installing libpcap [############################################################################] 100%
(102/112) installing libnfnetlink [############################################################################] 100%
(103/112) installing libnetfilter_conntrack [############################################################################] 100%
(104/112) installing iptables [############################################################################] 100%
^C05/112) installing kbd [----------------------------------------------------------------------------] 0%
Interrupt signal received
‣ Unmounting Package Cache...
umount: /var/tmp/mkosi-k7xvvu5s/root/var/cache/pacman/pkg: target is busy.
‣ Unmounting Package Cache complete.
‣ Unmounting image...
umount: /var/tmp/mkosi-k7xvvu5s/root/var/cache/pacman/pkg: target is busy.
‣ Unmounting image complete.
‣ Detaching image file...
‣ Detaching image file complete.
Traceback (most recent call last):
File "../mkosi/mkosi", line 5143, in <module>
main()
File "../mkosi/mkosi", line 5137, in main
run_verb(a)
File "../mkosi/mkosi", line 5114, in run_verb
build_stuff(args)
File "../mkosi/mkosi", line 4939, in build_stuff
raw, tar, root_hash = build_image(args, workspace, do_run_build_script=False, cleanup=True)
File "../mkosi/mkosi", line 4732, in build_image
install_distribution(args, workspace.name,
File "../mkosi/mkosi", line 2385, in install_distribution
install[args.distribution](args, workspace, do_run_build_script)
File "/usr/lib/python3.8/contextlib.py", line 75, in inner
return func(*args, **kwds)
File "../mkosi/mkosi", line 2183, in install_arch
run_pacstrap(packages)
File "../mkosi/mkosi", line 2180, in run_pacstrap
run(cmdline + list(packages), check=True)
File "../mkosi/mkosi", line 103, in run
raise KeyboardInterrupt()
KeyboardInterrupt
(105/112) installing kbd [############################################################################] 100%
Traceback (most recent call last):
File "/usr/lib/python3.8/weakref.py", line 642, in _exitfunc
f()
File "/usr/lib/python3.8/weakref.py", line 566, in __call__
return info.func(*info.args, **(info.kwargs or {}))
File "/usr/lib/python3.8/tempfile.py", line 818, in _cleanup
cls._rmtree(name)
File "/usr/lib/python3.8/tempfile.py", line 814, in _rmtree
_shutil.rmtree(name, onerror=onerror)
File "/usr/lib/python3.8/shutil.py", line 715, in rmtree
_rmtree_safe_fd(fd, path, onerror)
File "/usr/lib/python3.8/shutil.py", line 652, in _rmtree_safe_fd
_rmtree_safe_fd(dirfd, fullname, onerror)
File "/usr/lib/python3.8/shutil.py", line 652, in _rmtree_safe_fd
_rmtree_safe_fd(dirfd, fullname, onerror)
File "/usr/lib/python3.8/shutil.py", line 652, in _rmtree_safe_fd
_rmtree_safe_fd(dirfd, fullname, onerror)
[Previous line repeated 1 more time]
File "/usr/lib/python3.8/shutil.py", line 656, in _rmtree_safe_fd
onerror(os.rmdir, fullname, sys.exc_info())
File "/usr/lib/python3.8/shutil.py", line 654, in _rmtree_safe_fd
os.rmdir(entry.name, dir_fd=topfd)
OSError: [Errno 16] Device or resource busy: 'pkg'