How can I make fsck run non-interactively at boot time?

I have a headless Ubuntu 12.04 server in a datacenter 1500 miles away. Twice now on reboot the system decided it had to fsck. Unfortunately Ubuntu ran fsck in interactive mode, so I had to ask someone at my datacenter to go over, plug in a console, and press the Y key. How do I set it up so that fsck runs in non-interactive mode at boot time with the -y or -p (aka -a) flag?

If I understand Ubuntu's boot process correctly, init invokes mountall which in turn invokes fsck. However I don't see any way to configure how fsck is invoked. Is this possible?

(To head off one suggestion; I'm aware I can use tune2fs -i 0 -c 0 to prevent periodic fscks. That may help a little but I need the system to try to come back up even if it had a real reason to fsck, say after a power failure.)

In response to followup questions, here's the pertinent details of my /etc/fstab. I don't believe I've edited this at all from what Ubuntu put there.

UUID=3515461e-d425-4525-a07d-da986d2d7e04 /               ext4    errors=remount-ro 0       1
UUID=90908358-b147-42e2-8235-38c8119f15a6 /boot           ext4    defaults        0       2
UUID=01f67147-9117-4229-9b98-e97fa526bfc0 none            swap    sw              0       0

The setting I am looking for is in /etc/default/rcS, FSCKFIX=yes. This means "automatically repair filesystems with inconsistencies during boot" and causes fsck to run with the -y flag. It was set to no in both of my Ubuntu systems.

Even when set to no, the boot time fsck is still somewhat noninteractive. mountall runs fsck with -a, a synonym for -p, which means "automatically fix any filesystem problems that can be safely fixed without human intervention". Apparently -p drops to interactive mode if there are unsafe fixes to be made. To run fully automatically, you need -y or FSCKFIX=yes.

Here's the relevant bit of code from mountall.c

if (fsck_fix || mnt->fsck_fix) {
  NIH_MUST (nih_str_array_add (&args, NULL, &args_len, "-y"));
} else {
  NIH_MUST (nih_str_array_add (&args, NULL, &args_len, "-a"));
}

For Ubuntu 15,16,17+ the FSCKFIX value setting is located in lib/init/vars.sh

Can use command grep -r FSCKFIX * 2>/dev/null to fin it.

Make sure you don't have any flags that might cause this in fstab, and check your init scripts. (Try grep'ing your init scrips for 'fsck' to find where it's used) My system runs fsck non-interactive, so here is a copy of my fstab and part of my /etc/init/mountall script for you to compare

$ cat /etc/fstab
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
UUID=acbe3514-33a3-4170-b1be-df7b8460a49a /               ext4    errors=remount-ro 0       1
UUID=d361f696-7abc-11e1-9043-5711de71ade6 /home           ext4    defaults        0       2
UUID=213e032c-fce9-4e1b-9d64-0779f0db4208 none            swap    sw              0       0

Snippet from /etc/init/mountall

script
    . /etc/default/rcS
    [ -f /forcefsck ] && force_fsck="--force-fsck"
    [ "$FSCKFIX" = "yes" ] && fsck_fix="--fsck-fix"

    # set $LANG so that messages appearing in plymouth are translated
    if [ -r /etc/default/locale ]; then
        . /etc/default/locale
        export LANG LANGUAGE LC_MESSAGES LC_ALL
    fi

    exec mountall --daemon $force_fsck $fsck_fix
end script

How can I make fsck run non-interactively at boot time?

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