[systemd-devel] Requirements for successful mounting of RootImage?

[Topi Miettinen]

Hey,

I have this test.service unit:
[Unit]

[Install]
WantedBy=multi-user.target

[Service]
Type=oneshot
ExecStart=/bin/ls -lR
RootImage=/fs
MountAPIVFS=no

The file /fs has a MBR partition table:
Disk /dev/loop0: 1.1 MiB, 1192960 bytes, 2330 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x3990f3e6

Device       Boot Start   End Sectors  Size Id Type
/dev/loop0p1 *       34  2329    2296  1.1M 83 Linux

In the only partition a squashfs file system containing:
bin
bin/ls
boot
dev
etc
etc/group
etc/nsswitch.conf
etc/passwd
home
lib
lib64
lib64/ld-linux-x86-64.so.2
lib/libc.so.6
lib/libdl.so.2
lib/libpcre.so.3
lib/libpthread.so.0
lib/libselinux.so.1
media
opt
proc
root
run
sbin
srv
sys
tmp
usr
usr/bin
usr/lib
usr/lib64
usr/lib/x86_64-linux-gnu
usr/sbin
var
var/tmp

However, starting the service fails with abort:
Jul 30 13:25:42 machine systemd[1]: Starting test.service...
Jul 30 13:25:42 machine kernel:  loop0: p1
Jul 30 13:25:42 machine systemd[1]: test.service: Main process exited,
code=killed, status=6/ABRT
Jul 30 13:25:42 machine systemd[1]: Failed to start test.service.
Jul 30 13:25:42 machine systemd[1]: test.service: Unit entered failed state.
Jul 30 13:25:42 machine systemd[1]: test.service: Failed with result
'signal'.

It looks like systemd successfully mounts the file system, but then
suddenly aborts before even looking inside the file system:

2761  mount("/dev/loop1p1", "/run/systemd/unit-root", "squashfs",
MS_NODEV, NULL <unfinished ...>
2761  <... mount resumed> )             = 0
2761  rt_sigprocmask(SIG_UNBLOCK, [ABRT],  <unfinished ...>
2761  <... rt_sigprocmask resumed> NULL, 8) = 0
2761  rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1], [], 8) = 0
2761  getpid( <unfinished ...>
2761  <... getpid resumed> )            = 2761
2761  gettid( <unfinished ...>
2761  <... gettid resumed> )            = 2761
2761  tgkill(2761, 2761, SIGABRT <unfinished ...>
2761  <... tgkill resumed> )            = 0
2761  rt_sigprocmask(SIG_SETMASK, [],  <unfinished ...>
2761  <... rt_sigprocmask resumed> NULL, 8) = 0
2761  --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=2761,
si_uid=0} ---
2761  +++ killed by SIGABRT +++

The file system can be mounted by hand with losetup and mount, and
/bin/ls can be run from chroot. So I think everything should be OK but
RootImage still does not work and the error messages are useless.
Perhaps I miss some RootImage requirements? What exactly they are?

The same file system image without any partition table does not work either.

This is with Debian systemd version 234-2.

-Topi