Service Desk Knowledgebase: Linux

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This is the Linux content page of the CL Wiki Service Desk Knowledgebase. Its purpose is to provide information to the Service Desk team on how to handle problems and requests about this CL service. If you are involved with the provision of this CL service please feel free to add to the knowledge about that it.

If CL staff need to tell the Service Desk team about problems with this service please email
sys-admin-aside@cl.cam.ac.uk.

Return to the Service Desk Knowledgebase SERVICE PORTFOLIO

Key Service Description & URLs

CL Customer Documentation

Further CL Sys-Admin Resources

Underpinning Services

  • ??? - Any supporting or underpinning services

Customer-base for this Service

  • Linux boxes are available to all staff and post-graduates, and well as some on the Part III Under-graduates.

Costs

  • Hardware is charged for if you are a Research Assistant or a University Teaching Officer, but free to Post-graduates.
  • Support is free.

SLA

  • ??? - Timeframes or service level agreement for fulfilling the service

Service Desk Call Handling Procedure

  • RT tickets can be escalated to the unix-admin by changing the Queue to unix-admin with the Owner set to Nobody & Status set to new. Tell the requestor:
    I am passing this request over to our Unix Admin team who, I'm sure, will be in contact shortly.

Contacts

Primary

Other

Availability

  • Monday: 09:00-17:00
  • Tuesday: 09:00-17:00
  • Wednesday: 09:00-17:00
  • Thursday: 09:00-17:00
  • Friday: 09:00-17:00
  • Saturday: Closed
  • Sunday: Closed

Hints, Tips & Known Issues

Removing a broken install

Vince Woodley (17 Feb 2015)

ssh to the machine in question then...

1) Find the process responsible for the lock with sudo lsof /var/lib/dpkg/lock

2) Check for running dpkg processes with something like ps -ef | grep dpkg

3) Ask the requestor if they'd like you to kill it:
I suspect I could do that by killing the rogue process -- shall I have a go?

4) Kill any dpkg processes shown above with sudo kill 1234 etc...
If they refuse to die try sudo kill -HUG 1234

5) Check each is dead with the same command again sudo kill 1234 (hopefully there will be no such process)

6) Find the exact name of the dropbox package with dpkg -l \*dropb\* (or similar)

7) Remove it with cl-asuser apt-get remove nautilus-dropbox
(or similar) If that fails with:-
"dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct" then cd /var/lib/dpkg/updates and delete all the files there with rm *

8) Do an update of the system with cl-update-system

9) Check the output to make sure that everything's okay repeating cl-update-system if necessary

Clock slew problem

Graham Titmus (3 Feb 2015)

First check if this is a physical machine or a VM. If a physical machine login to it. If a Xen VM then login to it and check if it is tied to the dom0 clock. 

cat /proc/sys/xen/independent_wallclock

If that returns an error then proceed as for a standalone machine. If it returns 0 then you need to find the dom0 which hosts the VM, to find that do 

cl-onserver --xe cl-vm-status all hid | grep <<machine_name>>

When logged in to the appropriate machine (using ssh or in the case of Xen you could also connect via the Xen Centre guy) first check if it is working correctly 

/usr/sbin/ntpdc -p

which should not look like this 

 remote local st poll reach delay offset disp
 =======================================================================
 *LOCAL(0) 127.0.0.1 10 64 377 0.00000 0.000000 0.03046

but have multiple lines each to a remote ntp server.

If it does look like above then restart the ntpd service 

 cl-asuser service ntpd restart

and check the output again which should now look like 

remote local st poll reach delay offset disp
=======================================================================
=morgul.deadset. 128.232.26.100 16 64 0 0.00000 0.000000 4.00000
=time-b.as43289. 128.232.26.100 16 64 0 0.00000 0.000000 4.00000
=LOCAL(0) 127.0.0.1 10 64 1 0.00000 0.000000 2.81735
=ntp.katho.be 128.232.26.100 16 64 0 0.00000 0.000000 4.00000
=server.netkolik 128.232.26.100 16 64 0 0.00000 0.000000 4.00000
=ntp1d.cl.cam.ac 128.232.26.100 2 64 1 0.00070 0.002260 2.81735
=ntp1c.cl.cam.ac 128.232.26.100 2 64 1 0.00165 0.002201 2.81743
=ntp1b.cl.cam.ac 128.232.26.100 2 64 1 0.00121 0.003449 2.81743
=ntp1a.cl.cam.ac 128.232.26.100 2 64 1 0.00058 0.002520 2.81735

Linux user can't login using graphical interface

Graham Titmus (13 Jan 2015)

Symptoms: Linux user can't login using graphical interface, they enter username and password and get a blank screen then back to login

A common cause of this is a failure to access the home directory stored on the File Server (AKA Elmer or Filer), X (the window manager) needs to write a file there when it starts the user session. To diagnose if this is the problem do the following:-

  1. Remote login to the machine using ssh -K hostname@cl.cam.ac.uk from a CL machine - check if your home directory is present (ls -al ~). If is is look to see if the users home directory is present (ls -al ~crsid).
  2. If the home directory is missing then try to restart the auto mounter (cl-asuser service autofs restart).
  3. Look at the mounted filesystems (grep ldap /proc/mounts - will show which systems have been auto mounted using data form the LDAP).


An alternative is to ask the user to check if it is the machine failing to log them in or a problem with X by getting them to try on the text console (Select with Ctrl-Alt-F2). If they can login there but have no home then it is probably a problem with the filesystem. If they cannot login at all then it is an authentication problem. They should then try from another machine that is known to work to check their login works.

Adding privileged users

Machines are normally setup with the 'assigned user' having both cl-asuser and sudo access. They can use the latter to grant privileges to other users.

cl-asuser access: (if ACLs are enabled) is setup using sudo setfacl -m u:$CRSid:rw /etc/user-config/bundles where $CRSid should be replaced by the CRSid of the person who is to be granted privilege. cl-asuser privileges should then be available immediately.

sudo access: is setup by using an editor to add them to the relevant group (e.g. sudo or root) in the file /etc/group. To do this ssh -K $hostname and then:
cd /etc
sudo vi group [sudo] password for vrw10: Add the user's CRSid to the line like sudo:x:27:localadmin,sg692 by scrolling down to it with the arrow-keys and using [Shift]+A
to enter --- INSERT --- mode [ESC] out of insert mode Write and quit with :wg and [Enter]
sudo privileges will only take effect in new sessions.


If there are sudo problems use groups $CRSid to check which groups the user is in, and sudo -l -U $CRSid to check the status. Check /etc/sudoers and /etc/sudoers.d/* to check which groups give ALL access. If the assigned user has not been setup (because a machine has been moved to a new user or was not done when the machine was installed do cl-asuser cl-hostid-fix --user <<CRSid>> -a

Categorising Keywords

  • Linux Ubuntu PC Person Computer
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