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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 ?

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164

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.

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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 2:41
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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 7:21
80

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.)

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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 6 '15 at 17:55
  • I like mount --fake -a but it seems to return exit code($?)=0 always. Umm.. – kujiy Oct 3 '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 8:33
  • 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
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+150

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

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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 5 '20 at 3:18
  • 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 19 hours ago
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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
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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.

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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

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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 ~]#
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1

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

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

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