Devices time out at boot time but appear later

This document (7018491) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15 SP2
SUSE Linux Enterprise Server 15 SP1
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP4

SUSE Linux Enterprise Server 12 SP3

SUSE Linux Enterprise Server 12 SP2

SUSE Linux Enterprise Server 12 SP1
SUSE Linux Enterprise Server 12

Situation

The server drops to emergency mode at boot time and prompts to run journalctl -xb.

journalctl -xb shows the following types of errors:

Dependency failed for /export/data
Dependency failed for Local File Systems
Timed out waiting for device dev-mapper-export\x2ddata.device.

After logging into emergency mode, the device for /export/data mounts just fine and systemctl default continues and reaches the default target.
So the device is eventually found, but does not get found in time during the boot process.

Resolution

Add a device timeout tuning option (x-systemd.device-timeout) to /etc/fstab to give the device more time to appear.
For each of the devices in /etc/fstab more timeout is needed, add the device timeout option in the options field.
This option is parsed by the systemd-fstab-generator unit.

For example, change:

UUID=2ed453ee-c197-4e76-860b-d8ecf5540576 /export/data ext3 acl,user_xattr 1 2

to:

UUID=2ed453ee-c197-4e76-860b-d8ecf5540576 /export/data ext3 acl,user_xattr,x-systemd.device-timeout=300s 1 2

The systemd-fstab-generator(8) unit creates a mount unit for each entry in the /etc/fstab.
It will increase the time systemd waits for the device with this option.
In this case a 300 second / 5 minute timeout was added.

Cause

The disk devices take longer than usual to appear to the operating system, exceeding the default timeout value.

Additional Information

For debugging or testing purposes, the kernel parameter "systemd.default_timeout_start_sec=" can be set.
Once the timeout is determined, it can be specified in /etc/fstab with the x-systemd.device-timeout= option for the individual device.

Please note:
The parameter "systemd.default_timeout_start_sec=" overwrites the default start job timeout DefaultTimeoutStartSec= at boot.

It affects all units, ie not only the mount units generated from /etc/fstab.

Method to add the Kernel option (for debugging only):

Edit the /etc/default/grub and change:
GRUB_CMDLINE_LINUX=""
to this:
GRUB_CMDLINE_LINUX="systemd.default_timeout_start_sec=300s"
Run grub2-mkconfig -o /boot/grub2/grub.cfg and reboot.

This option will set a 5 minute timeout on all units, including mount units.

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