a start job is running for dev-disk-by

Recently, I encountered a strange problem when booting up my Linux OS.

a start job is running for dev-disk-by uuid <disk-partition-uuid>

This process lasts for 1 minute and 30s ! OMG! That’s unbearable. And then it told me:

Timed out waiting for device dev-disk-by\<disk-partition-uuid>
Denpendency failed for /dev/disk/by-uuid/<disk-partition-uuid>
Denpendency failed for Swap

Take a look at the third line. As you can clearly see, the disk partition causing this problem is the swap partition.

After my Linux OS booted into desktop, I opened up a terminal and check my swap partition with this command:

swapon --show

a start job is running for dev-disk-by

As you can see from the screenshot, my swap partition wasn’t activated. I also issued the following command to check mounted partitions and my swap partition wasn’t there.


So why did swap partition fail to mount on system boot time? As I later found out, the UUID of my swap partition has changed. Enter this command to check the real UUID of swap partition.

sudo blkid

then check the UUID of swap partition in /etc/fstab.

sudo nano /etc/fstab

If the two UUIDs are different, then the /etc/fstab file is corrupted and you need to replace the UUID in /etc/fstab with the UUID returned by sudo blkid.

Save and close /etc/fstab file. Reboot your computer.

Now the “a start job is running for dev-disk-by” message was gone and you saved 1 minute and 30s of your life.

The same error occurred on my Arch Linux, Fedora and Ubuntu machine. One thing I don’t like about Ubuntu is that it veils system messages with its logo when booting up. For a long time I did’t know why it takes such a long time for Ubuntu to boot into Unity desktop. Finally I found the reason.

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3 Responses to “a start job is running for dev-disk-by

  • I’m a Linux Newbie so my question might be hilarious.
    I haven’t settled on a distribution yet and want to try a few. Started out with Ubuntu a while back and now Xubuntu. I have an older spare system which I use as test environment. Currently only Win 10 (on sda) and Xubuntu (sdb). sda is a small disk, so I set it holds a Win10 partition, a data partition and a Windows swap partition. sdb is the bigger disk and I want my Linux distros on it. Installation of Xubuntu went like a charm and FAST (had to go with i386, because amd64 hung during install – some process wouldn’t start). Dual boot works fine. Anyhow, that’s what the system looks like.
    Here comes the question:
    I thought it would be smart to make a single swap partition for all Linux’es I will set up – meaning: they all should use the SAME partition. As I will only run one Linux at a time, one swap partition is all I need.
    Does that work that way – kind of automatically? Will all Linux’es recognize the swap partition as such (I set it up as Linux swap partition during Xubuntu installation)? Or will I have to tell that to each Linux (How?)?
    Your post triggered the thought that things might not be as simple as I imagine them to be.

    • Xiao Guoan
      8 years ago

      It is my understanding that most Linux distros will recognize your swap partition and automatically mount this swap partition when you install your distro on your computer. And of course you can allocate a single swap partition for all your Linux distros.

      You can always choose to manually edit partitions during installation which will give you the option to specify swap partition. And I recommend you to manually edit partitions during installation. Doing so you have more control over your system and you know exactly what your machine is doing.

      I wrote this post because the UUID of swap partition has changed and I don’t know how exactly this is possible. This doesn’t mean that Linux does not recognize swap partition. It means I have to modify the UUID in /etc/fstab file so Linux can find the swap partition using the right UUID and then mount it.

    • Robert Dinse
      6 years ago

      Although my understanding is that modern distributions will recognize it automatically, I still have some antique CentOS6 machines and so always specify it in /etc/fstab just to be sure.

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