mount can exit 0 (success) when it fails

[Scott Moser]

I'm on softlayer in an official Ubuntu image and 'mount' exits
success even when it fails.

$ cat /etc/cloud/build.info
build_name: server
serial: 20171116

$ cat /etc/fstab
LABEL=cloudimg-rootfs / ext4 defaults,relatime 0 0

# Added by Cloud Image build process
LABEL=cloudimg-bootfs /boot ext3 defaults,relatime 0 0
# CLOUD_IMG: This file was created/modified by the Cloud Image build process
# Mount the metadata disk for cloud-init, if present
LABEL=METADATA /var/lib/cloud/seed/config_drive vfat defaults,nofail 0 0
LABEL=SWAP-xvdb1 none swap sw,comment=cloudconfig 0 2

$ blkid
/dev/xvda1: LABEL="cloudimg-bootfs" UUID="63ea63a7-f64c-493c-90d4-384adc196be9" TYPE="ext3" PARTUUID="3276fc6f-01"
/dev/xvda2: LABEL="cloudimg-rootfs" UUID="82ca1e17-8bc2-4895-96bb-3c39e5863238" TYPE="ext4" PARTUUID="3276fc6f-02"
/dev/xvdh: SEC_TYPE="msdos" LABEL="config-2" UUID="9796-932E" TYPE="vfat"
/dev/xvdb1: LABEL="SWAP-xvdb1" UUID="d51fcca0-6b10-4934-a572-f3898dfd8840" TYPE="swap" PARTUUID="00025cdb-01"

$ whoami
root
$ grep /var/lib/cloud/seed/config_drive /proc/mounts
$ mount /var/lib/cloud/seed/config_drive
$ echo $?
0

## it exited 0 so it should be mounted, but it is not.
$ ls /var/lib/cloud/seed/config_drive
$ grep /var/lib/cloud/seed/config_drive /proc/mounts

## try somewhere else and with /dev/ path. it works.
$ mount /dev/xvdh /mnt
$ echo $?
0
$ grep /mnt /proc/mounts
/dev/xvdh /mnt vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 0
$ find /mnt/
/mnt/
/mnt/openstack
/mnt/openstack/latest
/mnt/openstack/latest/meta_data.json
/mnt/openstack/latest/network_data.json
/mnt/openstack/latest/user_data
/mnt/openstack/latest/vendor_data.json

$ journalctl -o short-monotonic --boot --no-pager | pastebinit
http://paste.ubuntu.com/26119983/

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: mount 2.27.1-6ubuntu3.3
ProcVersionSignature: Ubuntu 4.4.0-98.121-generic 4.4.90
Uname: Linux 4.4.0-98-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.12
Architecture: amd64
Date: Tue Dec 5 17:52:14 2017
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: util-linux
UpgradeStatus: No upgrade log present (probably fresh install)

[Scott Moser (smoser)]

I didn't notice initially but just did. The entry in /etc/fstab is bogus, containing a LABEL=METADATA but the disk here is LABEL=config-v2.

That is clearly broken, but 'mount' should not exit success.

[Ryan Harper (raharper)]

Can you attach:

  blkid output
  ls -al /dev/disk/by-label
  /proc/mounts

Testing locally on Xenial, and mount always says something isn't found.

% tail -n1 /etc/fstab
LABEL=METADATA /mnt vfat defaults, 0 0
(foudres) ~ % sudo mount -l -vvvv /mnt
mount: can't find LABEL=METADATA

strace of mount shows it consulting blkid for devices with LABEL

[Scott Moser (smoser)]

blkid output was above. and as I said in my first comment the entry in /etc/fstab is wrong.
there is no LABEL=METADATA device. So 'mount' *should* fail, but I would have expected it to exit non-zero.

I noticed just now that '/etc/fstab' has 'nofail' for that line. I removed that, and it fails as you show and as expected. So the issue here is really just 2 things

a.) the Canonical provided image has a bogus and confusing entry in /etc/fstab
b.) mount really should not exit '0' when explicitly asked to mount something even if it has 'nofail'.

heres the info you asked for:

$ mount -l -vvv /var/lib/cloud/seed/config_drive; echo $?
0

$ blkid
/dev/xvda1: LABEL="cloudimg-bootfs" UUID="63ea63a7-f64c-493c-90d4-384adc196be9" TYPE="ext3" PARTUUID="3276fc6f-01"
/dev/xvda2: LABEL="cloudimg-rootfs" UUID="82ca1e17-8bc2-4895-96bb-3c39e5863238" TYPE="ext4" PARTUUID="3276fc6f-02"
/dev/xvdh: SEC_TYPE="msdos" LABEL="config-2" UUID="9796-932E" TYPE="vfat"
/dev/xvdb1: LABEL="SWAP-xvdb1" UUID="d51fcca0-6b10-4934-a572-f3898dfd8840" TYPE="swap" PARTUUID="00025cdb-01"

$ cat /proc/mounts
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
udev /dev devtmpfs rw,nosuid,relatime,size=483664k,nr_inodes=120916,mode=755 0 0
devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,nosuid,noexec,relatime,size=101204k,mode=755 0 0
/dev/xvda2 / ext4 rw,relatime,data=ordered 0 0
securityfs /sys/kernel/security securityfs rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
tmpfs /run/lock tmpfs rw,nosuid,nodev,noexec,relatime,size=5120k 0 0
tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,mode=755 0 0
cgroup /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd 0 0
pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0
cgroup /sys/fs/cgroup/cpu,cpuacct cgroup rw,nosuid,nodev,noexec,relatime,cpu,cpuacct 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,nosuid,nodev,noexec,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/net_cls,net_prio cgroup rw,nosuid,nodev,noexec,relatime,net_cls,net_prio 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,nosuid,nodev,noexec,relatime,perf_event 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,nosuid,nodev,noexec,relatime,devices 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,nosuid,nodev,noexec,relatime,memory 0 0
cgroup /sys/fs/cgroup/hugetlb cgroup rw,nosuid,nodev,noexec,relatime,hugetlb 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,nosuid,nodev,noexec,relatime,freezer 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
systemd-1 /proc/sys/fs/binfmt_misc autofs rw,relatime,fd=37,pgrp=1,timeout=0,minproto=5,maxproto=5,direct 0 0
mqueue /dev/mqueue mqueue rw,relatime 0 0
none /proc/xen xenfs rw,relatime 0 0
fusectl /sys/fs/fuse/connections fusectl rw,relatime 0 0
/dev/xvda1 /boot ext3 rw,relatime,data=ordered 0 0
lxcfs /var/lib/lxcfs fuse.lxcfs rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other 0 0...