Tag: Linux

Specifically Linux related things

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How to check filesystems in a qcow2 image

A useful post how to fsck (check and fix) a filesystem in a qcow2 image (as typically used for KVM VMs, e.g. in Proxmox):

How to recover a qcow2 file using fsck

On Proxmox or Debian, one does the following:

Attention:

  • Make sure the according VM isn’t running, i.e. the partition not mounted
  • Adjust the commands below to match your system, use the correct qcow2 image, use the correct fsck-variant, fsck the correct filesystem, note that -p tries to automatically fix errors!
# modprobe nbd max_part=8
# qemu-nbd --connect=/dev/nbd0 /var/lib/vz/images/100/vm-100-disk-1.qcow2
# fdisk -l /dev/ndb0
/dev/nbd0p1            2048     7813119     3905536   82  Linux swap / Solaris
/dev/nbd0p2   *     7813120   119537663    55862272   83  Linux
# fsck.ext4 /dev/nbd0p2
# fsck.ext4 -p /dev/nbd0p2
# qemu-nbd --disconnect /dev/nbd0

Like this, one doesn’t need to boot the VM using a boot ISO/CDROM and can fix the filesystem right from the host node.

 

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zpool: Symbol `spa_feature_table’ has different size in shared object, consider re-linking

If you see the following error message when executing ‘zpool status’ after “upgrading” Proxmox to the (currently) latest version with ZoL 0.6.4 instead of 0.6.3:

zpool: Symbol `spa_feature_table' has different size in shared object, consider re-linking

Explanation:

“Re-linking” doesn’t have a special meaning in ZFS/ZoL terminology, it rather just describes the usual linking step after compiling some source code.

Solution:

The most likely cause is that some new, updated and required packages have not been installed (e.g. with ‘uname -a’, you’ll see that the old kernel is still running, even after rebooting). Usually, this happens if one executes “apt-get update && apt-get upgrade” (as usual) rather than “apt-get update && apt-get dist-upgrade“. So, in order to solve this problem, do:

# apt-get update && apt-get dist-upgrade
# reboot

In this case, ZoL 0.6.4 also includes a couple of new features which can be enabled for all local ZFS pools by executing:

# zpool upgrade -a
This system supports ZFS pool feature flags.

Enabled the following features on 'rpool':
 spacemap_histogram
 enabled_txg
 hole_birth
 extensible_dataset
 embedded_data
 bookmarks
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Using IRC on the go

Running the console IRC client weechat (not to confuse with the wechat messenger) in a screen or tmux session on a Linux (or Mac OS X) server and accessing it trough mosh is a great way to use IRC on the go, i.e. with a unsteady Internet connection.

P.S. Thanks to Devaux and rmeyer for the hints

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Delete duplicate e-mail messages

If you need to delete duplicate e-mail messages on an IMAP server, take a look at this useful IMAP de-duplicator script:

IMAP de-duplicator – IMAPdedup

As IMAPdedup is a command line interface tool (a python script), it’s particularly useful for:

  • automated deletion of duplicates (as it can be called from other scripts)
  • extraordinarily big mailboxes or if you have many subfolders (as there’s no intervention by the user required)
  • if you have console/shell access to the IMAP server (as you can then run the script on the server itself, speeding the de-duplication process further up)

I also found that it deals relatively well with failures (e.g. when a folder is read-only and hence messages can’t be deleted): It simply reports them on the screen and carries on.

Here’s a quick’n’dirty bash script to de-dup the inbox and all subfolders of the specified account:

#!/bin/sh
# Delete all duplicate messages in all folders of said account.
# Note that we connect through SSL (-x) to the default port.

SERVER="my.server.com"
USER="mylogin"
PASS="mypass"

for folder in `imapdedup.py -s $SERVER -x -u $USER -w $PASS -l`;
do
 imapdedup.py -s $SERVER -x -u $USER -w $PASS $folder
done

If you only have to de-duplicate messages in a small folder, you could also use the following de-duplication add-on for Mozilla Thunderbird:

Remove Duplicate Messages Add-on for Thunderbird

Note however that the ‘Remove Duplicate Messages’ add-on is intended for interactive use only, not for batch processing. I also noticed that it fails at cleaning big mail folders (e.g. containing 50’000 messages).

 

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Moving Zimbra Collaboration Server to a new IP address

Here’s a quick overview how to migrate a ZCS mail server (based on Ubuntu) to a new IP address:

0) Not covered here: Adjusting DNS entries. Make sure you lower the TTLs of the relevant DNS entries a couple of days in advance in order to minimize downtime for clients (e.g. set a TTL of 300 for a 5 minute downtime).

1) Set the new IP address in:
* The relevant DNS entries
* /etc/network/interfaces
* /etc/hosts
* If ZCS runs in a container/VM, don’t forget to adjust its IP address too.

2) If the new IP address is part of a new subnet, make sure to add this new subnet to ZCS’s trusted_networks, otherwise, sending (relaying) messages through ZCS from Zimbra Desktop (or any other mail client) won’t work[1]. This can be set using ZCS’s web admin interface (i.e. https://mail.myserver.com:7071/zimbraAdmin/):
Navigate to “Server settings”, then open the “MTA” tab and set something analogous to the following in “MTA Trusted Networks”:
127.0.0.0/8 w.x.y.z/26

3) Restart networking and the ZCS services (it’s important, as this adjusts the trusted_network setting in ZCS’s amavisd too):
# /etc/init.d/zimbra stop
# /etc/init.d/networking restart
# /etc/init.d/zimbra start

Alternatively, just reboot the server, particularly if it runs in a VM.

Voilà!

Note: The need for the adjustments in step 2) might come as a surprise. Authenticated messages to be relayed through ZCS apparently seem to originate from the external IP address, not localhost/127.0.0.1.

[1] A typical postfix error message might look like:
Delivery Failure Notification: Invalid address: somebody . com.zimbra.cs.mailbox.MailSender$SafeSendFailedException: MESSAGE_NOT_DELIVERED; chained exception is: com.zimbra.cs.mailclient.smtp.InvalidRecipientException: RCPT failed: Invalid recipient somebody@somedomain.com: 554 5.7.1 : Relay access denied