Resume device. What is it?

Willy Hamra w.hamra1987 at gmail.com
Tue Mar 31 16:46:44 UTC 2009


2009/3/31 Nigel Henry <cave.dnb2m97pp at aliceadsl.fr>:
> On Tuesday 31 March 2009 16:09, Willy Hamra wrote:
>> 2009/3/31 Howard Coles Jr. <dhcolesj at gmail.com>:
>> > On Monday 30 March 2009 01:20:04 pm Nigel Henry wrote:
>> >> On Monday 30 March 2009 18:52, Antonio Augusto (Mancha) wrote:
>> >> > Hey Nigel,
>> >> >
>> >> > For what i get your problem MIGHT be, indeed, related to UUID. UUID is
>> >> > used as a "symbolic" name to a device, so you ca use it instead of
>> >> > /dev/sda3 (which might change when you repartition your disk).
>> >> > What might be happening is that the UUID of /dev/sda3 was changed
>> >> > (maybe by the new install of F10?) and hence none of your OSs can find
>> >> > it. You can check this by looking at /dev/disk/by-uuid and seeing if
>> >> > there is a syn-link there pointing to /dev/sda3, if there is check if
>> >> > its the same name as used in /etc/fstab.
>> >> >
>> >> > The reason you see 0Mb swap may be because the UUID can't be found,
>> >> > and hence no swap is activated.
>> >> >
>> >> > To your other question: yes you can simple comment that line in fstab
>> >> > and replace it with the one form arch.
>> >> >
>> >> > Also, then you see "resume device", usually it refers to the partition
>> >> > used to store the contents of the RAM when you put your computer to
>> >> > hibernate (suspend do disk). Linux uses the swap space to store the
>> >> > contents of the RAM, so it can resume when booted.
>> >> > When you see a message like "waiting for resume device" or "resume
>> >> > device not found", it simply means that Linux was not suspended to
>> >> > disk, and is doing a cold boot. Nothing wrong with that.
>> >> >
>> >> > If you have any more questions please post them.
>> >> >
>> >> > Cheers,
>> >> > KM
>> >>
>> >> Hi Antonio.
>> >>
>> >> Thanks for your reply. Having booted up a few other distros on this
>> >> machine, so as to post output on my previous post to the list, I've just
>> >> tried F10 again, which now boots up ok (No real surprise, as I often
>> >> have problems with this Asus M2N-X Plus mobo). That said, fstab output
>> >> from F10 is below, and /, and /home have UUID's, but swap is accessing
>> >> /dev/sda3, and Gkrellm is showing 2000M-2000M free, which is correct.
>> >> F10 was the last distro installed on this machine.
>> >>
>> >> #
>> >> # /etc/fstab
>> >> # Created by anaconda on Mon Feb 16 21:08:47 2009
>> >> #
>> >> # Accessible filesystems, by reference, are maintained under '/dev/disk'
>> >> # See man pages fstab(5), findfs(8), mount(8) and/or vol_id(8) for more
>> >> info #
>> >> UUID=bd4e6a39-e802-44d4-9fd0-fc22692770b0 /                       ext3
>> >> defaults        1 1
>> >> UUID=5d6d96b6-c815-4816-8bce-81c286210754 /home                   ext3
>> >> defaults        1 2
>> >> tmpfs                   /dev/shm                tmpfs   defaults
>> >>  0 0 devpts                  /dev/pts                devpts
>> >>  gid=5,mode=620  0 0 sysfs                   /sys
>> >>  sysfs   defaults        0 0 proc                    /proc
>> >>     proc    defaults        0 0 /dev/sda3               swap
>> >>        swap    defaults        0 0
>> >>
>> >> /dev/sdb1               /mnt/sdb1               vfat    auto,umask=0
>> >>  0 0 /dev/sdb2               /mnt/sdb2               vfat
>> >>  auto,umask=0    0 0
>> >>
>> >>
>> >>
>> >> Now a reboot into Kubuntu Intrepid 8.10, and with an edit to fstab,
>> >> changing the UUID for swap to /dev/sda3, this appears to be ok after a
>> >> reboot. See below for fstab output.
>> >>
>> >> # /dev/sda3
>> >> #UUID=a2bc95ec-5fe4-4651-9ca5-7027344141e3 none            swap    sw
>> >> 0       0
>> >>
>> >> #Swap reference changed by me
>> >> /dev/sda3             none           swap           sw       0 0
>> >>
>> >> The above appears to have resolved the problem. On bootup with Intrepid,
>> >> the bootup still hangs at the "waiting for resume device" line for a
>> >> couple of seconds, but I'll let that go. At least Gkrellm now shows that
>> >> swap is on.
>> >>
>> >> Tried sudo swapoff /dev/sda3, and Gkrellm showed swap as 0M, then did
>> >> sudo swapon /dev/sda3, and Gkrellm showed swap as 2000M-2000M free.
>> >>
>> >> Thanks again for your reply Antonio.
>> >>
>> >> Nigel.
>> >>
>> >> > On Mon, Mar 30, 2009 at 13:26, Nigel Henry
>> >> > <cave.dnb2m97pp at aliceadsl.fr>
>> >>
>> >> wrote:
>> >> > > I booted up F10 this morning, after fixing an selinux related
>> >> > > problem yesterday, but the bootup stalled. I noticed an entry on the
>> >> > > bootup messages, "unable to stat resume device". Not wishing to
>> >> > > waste time on F10, as I'd had enough of that yesterday, I rebooted
>> >> > > to Kubuntu Intrepid (on the same machine), and Intrepid hung for a
>> >> > > few seconds with "waiting for resume device", then the bootup
>> >> > > continued with no problems.
>> >> > >
>> >> > > I googled "resume device", and there are a whole bunch of hits, with
>> >> > > folks having various problems with it. It appears to be referencing
>> >> > > "swap", but why resume device. I would have thought that, that
>> >> > > description applied more to laptops, and my machine is a PC.
>> >> > >
>> >> > > Nigel.
>> >
>> > Nigel, look in the boot.cfg or /boot/grub/menu.lst for an entry called
>> > "resume=<some device>"  Make it match either with the UUID or the /dev/
>> > id name and you should be good or just remove it altogether (as mine is)
>> > and the OS should find it by default.  This entry tells the Kernel were
>> > to look for a resumable instance of the OS whether to RAM (suspend) or to
>> > Disk (Hibernate).
>>
>> i believe this entry is in "/etc/initramfs-tools/conf.d/resume"
>> i've had to edit this file many times, nowadays i use a link from
>> /dev/disk/by-id in that file, since i always run mkswap which changes
>> my swap's UUID.
>>
>>
>> --
>> Willy K. Hamra
>> Manager of Hamra Information Systems
>> Co. Manager of Zeina Computers and Billy Net.
>
> Hi Willy.
>
> Thanks for that info. I found nothing in /boot/grub/menu.lst, when my googling
> "resume device" yesterday, suggested looking there. I also, today checked
> out /dev/disk/by-uuid, which Antonio suggested, but no symlink there
> to /dev/sda3 (swap partition). /etc/initramfs-tools/conf.d has the resume
> file. Just one line in it, as below.
> RESUME=UUID=a2bc95ec-5fe4-4651-9ca5-7027344141e3
>
> That matches the UUID in /etc/fstab  for the swap partition, but I assume that
> because there is no symlink to /dev/sda3 in /dev/disk/by-uuid, that is the
> reason why the UUID entry in /etc/fstab was unable to switch on the swap. I
> fixed it as below, and perhaps it's a hack, but swap is now being switched on
> at bootup.
>
>  # /dev/sda3
>  #UUID=a2bc95ec-5fe4-4651-9ca5-7027344141e3 none            swap    sw
>  0       0
>
>  #Swap reference changed by me
>  /dev/sda3             none           swap           sw       0 0
>
> It's getting a bit academic now. All my machines are PC's. I may be wrong, but
> it appears that this resume device is something specific to laptop users,
> where when you shut the lid, whatever is in the physical RAM, is saved to the
> swap partition, then when you reopen the lid, the resume device is brought
> into play, and you see things as they were before you closed the lid. I'm not
> a laptop user, so please excuse any errors above.
>
> Is it possible to prevent the machine when booting up, looking for this resume
> device, when you are not using a laptop? I'd already switched laptop-mode off
> ages ago, using sysv-rc-conf.
>
> I'd searched /etc/initramfs-tools earlier, but somehow missed the resume file.
> I'd also had a good look in /etc/udev, but couldn't find any rules relating
> to the creation of these UUID symlinks to the block devices, but perhaps they
> are created by the initrd before udev is run.
>
> While googling I did see some suggestions that to resolve the resume device
> problem, it was necessary to edit the initrd file, but I've never messed with
> that, yet.
>
> As I say, this is now going a bit academic, but any comments are welcome.
>
> Nigel.
>

what u said is correct, but desktop users like me also use it when i
need to hibernate the computer :)
what u did to the swap partition in fstab is correct, as long as u
keep in mind not to add/remove hard disks.
i have my kubuntu on sdb, so once i removed my sda to lend to some
friend, and kubuntu blindly wrote swap on a partition on  sdc which
became sdb after removing sda, it corrupted the partition, after that,
i learned to use /dev/disk/by-id, which is guaranteed to always point
to the correct hard disk.
i advise you to read "man initramfs-tools" a bit to get a general info
about what's going n, some of it is hard to understand, just skim
through it.
at one point, it states that resume capability is set in a script
called "init" located in /usr/share/initramfs-tools/
i found it at line 119, a statement that looks like noresume=y . now
this confused me a bit since i always resume, yet the script says that
noresume is true, so not sure what this parameter does. someone else,
might be able to help you from here onwards :)

-- 
Willy K. Hamra
Manager of Hamra Information Systems
Co. Manager of Zeina Computers and Billy Net.




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