how to debug problem with "failing unmounting"

how to debug problem with "failing unmounting"

[Tomek The Messenger]

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Hi
On the soc on which I work there is issue with unmouting some
partitions/directories during /sbin/reboot, here is some example:

[   OK   ]  Stopped target Local File System.
Unmouting Temporary Directory (/tmp)...
Unmouting /run/user/0...
...
[   FAILED  ]  Failed unmouting Temporary Directory (/tmp).
[   FAILED  ]  Failed unmouting  /run/user/0.
....

Unfortunately like it is typical in kernel information about why
unmouting failed doesn't appear.  So seems like searching in darkness what
is going on. Is any way how to search in darkness? Firstly I should make
sure /tmp or /run/user/0 is really a partition and was mount at linux
startup. Then maybe I should check access rights if it is rwx. What else
can be tried here?

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Re: how to debug problem with "failing unmounting"

[Abu Rasheda]

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On Thu, Jul 9, 2020 at 5:24 AM Tomek The Messenger <
tomekthemessenger@gmail.com> wrote:

> Hi
> On the soc on which I work there is issue with unmouting some
> partitions/directories during /sbin/reboot, here is some example:
>
> [   OK   ]  Stopped target Local File System.
> Unmouting Temporary Directory (/tmp)...
> Unmouting /run/user/0...
> ...
> [   FAILED  ]  Failed unmouting Temporary Directory (/tmp).
> [   FAILED  ]  Failed unmouting  /run/user/0.
> ....
>
> Unfortunately like it is typical in kernel information about why
> unmouting failed doesn't appear.  So seems like searching in darkness what
> is going on. Is any way how to search in darkness? Firstly I should make
> sure /tmp or /run/user/0 is really a partition and was mount at linux
> startup. Then maybe I should check access rights if it is rwx. What else
> can be tried here?
> _______________________________________________
>
> make sure there is no process which has these directories open (cd into it
or open a file), you can I put some printk in the code to debug what leads
to this condition.

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Re: how to debug problem with "failing unmounting"

[Valdis Klētnieks]

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On Thu, 09 Jul 2020 14:22:00 +0200, Tomek The Messenger said:

> On the soc on which I work there is issue with unmouting some
> partitions/directories during /sbin/reboot, here is some example:
>
> [   OK   ]  Stopped target Local File System.
> Unmouting Temporary Directory (/tmp)...
> Unmouting /run/user/0...
> ...
> [   FAILED  ]  Failed unmouting Temporary Directory (/tmp).
> [   FAILED  ]  Failed unmouting  /run/user/0.
> ....
>
> Unfortunately like it is typical in kernel information about why
> unmouting failed doesn't appear. 

Those aren't kernel messages, they're messages issued by your init system.
(Based on OK/FAILED, you're probably using a sysvinit rather than systemd, and
the messages are coming from scripts in /etc/rc.d/rc6/ which is the 'reboot'
runlevel - rc6 has symlinks to the actual script.  The main shutdown/reboot
script basically does a 'for $script in /etc/rc.d/rc6; do $script stop; done'.

The most common reason for a filesystem to fail to unmount is that a process still
has a file open on the file system.

And for this, lsof is your friend.   Stick an '/bin/lsof /tmp' in the script at the appropriate
place to find out what's still got /tmp busy.

(Depending on the system, it may not be worth looking into - often /tmp
and /run are tmpfs systems that are going to evaporate *anyhow*, so there's
no actual danger of a filesystem or data getting corrupted due to a hard
dismount while the file system is active)

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