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I modified /etc/fstab.

I verified the new devices and I can mount them with the mount command.

How may I validate the modifications made to /etc/fstab ?

Luc M
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8 Answers8

190

You can simple run: mount -a

-a Mount all filesystems (of the given types) mentioned in fstab.

This command will mount all (not-yet-mounted) filesystems mentioned in fstab and is used in system script startup during booting.

Prix
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    ...and compare it to /etc/mtab once you've done a "sudo mount -a", just to make sure all your options have been honoured. – adebaumann Aug 25 '10 at 10:25
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    `mount -a` by rereading `/etc/fstab` would also reload `/etc/mtab` so he should be fine with that only. – Prix Aug 26 '10 at 02:41
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    isn't that the point which adebaumann is trying to raise here? mount -a might return success, but doesn't necessarily mean that all the specific mount options have been honoured. since this will also reload /etc/mtab, you should check to see if all option are working? – RapidWebs Jun 28 '14 at 07:21
  • You may need to run a "systemctl daemon-reload" before this. Mount uses systemd's view of the world and if that is not updated you will just be loading what was present at last boot – m12lrpv Dec 22 '21 at 07:37
93

The mount command take an --fake or -f for short. The following command should do what you need:

mount -fav

The following is in the documentation for -f option:

Causes everything to be done except for the actual system call; if it's not obvious, this ``fakes'' mounting the filesystem. This option is useful in conjunction with the -v flag to determine what the mount command is trying to do.

(Note this is Linux - check before using elsewhere: FreeBSD uses -f for 'force' - exactly the opposite meaning.)

Paul
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tronda
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    mount -fav doesn't check that device with specified UUID is actually in the system. Also one would like to combine -f with -n not to pollute /etc/mtab – Alexandr Priymak Feb 06 '15 at 17:55
  • I like `mount --fake -a` but it seems to return `exit code($?)=0` always. Umm.. – kujiy Oct 03 '18 at 11:54
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    Also the fake option does not check whether the directory exists. It says `successfully mounted` even when the mount point dosent exist – DollarAkshay Nov 23 '18 at 08:33
  • This seems to be a good first thing to try, but you should also do a "mount -a" afterwards to verify. In my case, I set the options to "default" instead of "defaults" (which was preventing my Pi from booting), but `mount -fav` validated it as correct. As soon as I did a `mount -a` it found an error. – Adam Plocher Aug 11 '19 at 20:42
  • work with me `"Debian GNU/Linux 11 (bullseye)"` – Tiana987642 Jul 28 '22 at 15:24
71

sudo findmnt --verify --verbose is the best way I've found

rockwotj
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    Amazing answer. I'd never heart of findmnt before, but it's really fully-featured and part of util-linux! – ACK_stoverflow May 05 '20 at 03:18
  • `findmnt` told me that `fuse.sshfs seems unsupported by the current kernel`, which is not true because I was able to mount the sshfs share with `mount -a` – user84207 Mar 08 '21 at 03:10
  • this could not detect typos XD `errors=remout-ro` for example, i have to boot using another live cd to investigate – Kokizzu Jun 25 '22 at 06:09
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Note that if you add a swap file to your fstab, mount -a won't turn it on: you'll want to run swapon -a.

Ian Hunter
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I found this /problem/ but the solution didn't meet my requirements.

When rebooting with any invalid entries in the /etc/fstab, such as missing file systems that fsck cannot check; the system will fail to boot. That can be much more difficult to deal with if you have a headless box.

This is my solution to checking /etc/fstab to avoid this boot problem:

    # cat /usr/local/bin/check-fstab-uuid-entries.sh
    #!/usr/bin/env bash

    for x in $(grep ^UUID /etc/fstab|cut -d \  -f 1|cut -d = -f 2)
    do
            if [ ! -h /dev/disk/by-uuid/$x ];then
                    echo $(grep $x /etc/fstab)  ..... not found
            fi
    done
Andrew McGlashan
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  • Nice script, but can you please explain what it does? – Peter Wippermann Jan 28 '22 at 21:10
  • @PeterWippermann Well, it just checks fstab entries using UUID to make sure the volume is available; if it wasn't available then boot would stop and require intervention to continue. I think other options might be better, like `mount -fav` ... – Andrew McGlashan Jan 30 '22 at 05:18
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TBH even fake mounting doesn't safely validate the fstab for bad fs type entries.

you can have entries that have correct uuid's, directories etc but if you specify a noexistant FS type this will halt your boot next time.

[root@grumpy ~]# grep backup /etc/fstab
UUID=5ed48e5e-7251-4d49-a273-195cf0432a89       /mnt/backup     noatime,nodiratime,xfs defaults,nodev,nosuid    0 0
[root@grump ~]#

[root@grumpy ~]# mount -fav | grep backup
/mnt/backup              : successfully mounted
[root@grumpy ~]#
OldTimeAdmin
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mount -a is safe method to check /etc/fstab otherwise wrong entry could break the system

It is also advised to keep a backup copy of original /etc/fstab file. it could be copied to home directory of root

Vikas Avnish
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I open another term or tab and run: tail -f /var/log/kern.log

Sometimes errors show there that don't show when mounting.

clay
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