BASH if statements: ‘too many arguments’ error

Posted by Christian Ashby on April 28, 2010

If you are writing a BASH script which searches for a file pattern in a folder using this syntax:

[-f {pattern}]

Instead, use the following syntax:

files=$(ls {pattern} 2> /dev/null | wc -l)
if [ "$files" != "0" ]

This can be replaced with a similar command using find if required.


 

Debian: apt-get interrupted, leaves files in bad state

Posted by Christian Ashby on April 19, 2010

For those using Debian or Ubuntu Linux, there are situations where the package management system can leave files open if a certain package fails, or if you cancel the installation using CTRL+C, you may see the following error when you try another package installation:

debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable

Using the following command will tell you what’s using it:

fuser -v /var/cache/debconf/config.dat

This will give you the process ID in the right-hand column. You can then use kill {process ID} to remove this process and re run your apt-get command.


 

Converting open-source Xen Windows VMs to XenServer

Posted by Christian Ashby on April 13, 2010

A number of people are looking to migrate from the open-source Xen to Citrix XenServer itself, and it’s not immediately obvious how to migrate Windows VMs between the two platforms. Citrix have a tool called ‘XenConvert’ designed to move machines between environments, and the way you can use this to move from open-source Xen is as follows:

  • Download XenConvert from the Citrix downloads centre.
  • Add a virtual disk to the guest machine (at least twice the size of the existing disk) to receive the exported VM.
  • Run the original guest machine and partition / format the new virtual disk (NTFS / FAT, as long as you can mount these filesystems in the host).
  • Install & Run XenConvert on the source guest machine.
  • Select ‘XVA’ and select the new virtual disk as the destination for the XVA image.
  • Shut down the source guest machine.
  • Work out where the new virtual partition starts – something like this:
    root@host:/etc/xen# parted /dev/host-vm/name-XVA
    GNU Parted 1.7.1
    Using /dev/mapper/host--vm-name--XVA
    Welcome to GNU Parted! Type 'help' to view a list of commands.
    (parted) unit B
    (parted) print
    
    Disk /dev/mapper/host--vm-name--XVA: 26843545599B
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    
    Number  Start   End           Size          Type     File system  Flags
    1      32256B  26839088639B  26839056384B  primary  ntfs
  • Mount the new virtual disk – change ‘offset’ to be the value in the Start column above, replace ntfs with vfat if FAT32 was used:
    mount -o ro,offset=32256 -t ntfs /dev/host-vm/name-XVA /mnt/t
  • Copy the *.xva folder from this mounted drive to somewhere accessible to the new XenServer host.
  • Run XenCenter on a machine and connect to the new host.
  • Import a new VM, select the ova.xml file from the *.xva folder, and follow the import – you’ll need to setup a new Network Interface.
  • If required, reactivate Windows on the new guest as it starts up, and install XenServer Tools.

 

Oracle XE: Clearing out unwanted trace files

Posted by Christian Ashby on April 9, 2010

If left unchecked, Oracle XE installations can balloon in size quite quickly – this is due to the trace files being written by the server. The following run in a cron script can be used to remove files more than 7 days old.

#!/bin/bash
find $ORACLE_HOME/../../../admin/$ORACLE_SID/bdump -name "*.trc" -mtime +7 -exec rm "{}" \;
find $ORACLE_HOME/../../../admin/$ORACLE_SID/udump -name "*.trc" -mtime +7 -exec rm "{}" \;
find $ORACLE_HOME/../../../admin/$ORACLE_SID/cdump -name "*.trc" -mtime +7 -exec rm "{}" \;

This tip was found and modified for XE in the following a useful article ‘Oracle Linux – Using the “find” command to manage files’.


 

Blocking Internet Explorer updates

Posted by Christian Ashby on April 2, 2010

If you are developing websites, or simply don’t want to change browsers, you can stop Microsoft automatic update from installing IE 7 or IE 8 by installing the following updates from Microsoft:

Once run, they will extract files to the location of your choice, then you have to use an elevated command prompt and run the command with a /B switch (block) as follows:

IE70Blocker.cmd /B

You can revert to the normal state (allowing Microsoft / Windows Update to replace your browser) as follows:

IE70Blocker.cmd /U

Note that in order to keep IE6 you need to run both 7 and 8 blockers.

Then, you can keep your system completely up to date whilst maintaining the old-school browsers!