Notes about open source software, computers, other stuff.

Tag: network (Page 1 of 2)

Using rsync to backup a ZFS file system to a remote Synology Diskstation

Some time ago I moved from using LVM to using ZFS on my home server. This meant I also had to change the backup script I used to make backups on a remote Synology Diskstation. Below is the updated script. I also updated it such that it now needs a single command line argument: the hostname of the Diskstation to backup to (because I now have two Diskstations at different locations). If you want to run this script from cron you should set up key-based SSH login (see also here and here).

# This script makes a backup of my home dirs to a Synology DiskStation at
# another location. I use ZFS for my /home, so I make a snapshot first and
# backup from there.
# This script requires that the first command line argument is the
# host name of the remote backup server (the Synology NAS). It also
# assumes that the location of the backups is the same on each
# remote backup server.
# Time-stamp: <2014-10-27 11:35:39 (L.C. Karssen)>
# This script it licensed under the GNU GPLv3.
set -u
if [ ${#} -lt 1 ]; then
    echo -n "ERROR: Please specify a host name as first command" 1>&2
    echo " line option" 1>&2
    exit -1
# Some settings
# Options for the remote (Synology) backup destination
# Options for the client (the data to be backed up)
# ZFS options
# Backup source path. Don't forget to have trailing / otherwise
# rsync's --delete option won't work
# rsync options
OPTIONS="--delete -azvhHSP --numeric-ids --stats"
OPTIONS="$OPTIONS --timeout=60 --delete-excluded"
OPTIONS="$OPTIONS --skip-compress=gz/jpg/mp[34]/7z/bz2/ace/avi/deb/gpg/iso/jpeg/lz/lzma/lzo/mov/ogg/png/rar/CR2/JPG/MOV"
EXCLUSIONS="--exclude lost+found --exclude .thumbnails --exclude .gvfs"
EXCLUSIONS="$EXCLUSIONS --exclude .cache --exclude Cache"
EXCLUSIONS="$EXCLUSIONS --exclude .local/share/Trash"
EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/tmp/Downloads/*.iso"
EXCLUSIONS="$EXCLUSIONS --exclude home/lennart/.recycle"
EXCLUSIONS="$EXCLUSIONS --exclude _dev_dvb_adapter0_Philips_TDA10023_DVB*"
# The real work
# Create the ZFS snapshot
if [ -d $SNAPDIR ]; then
    # If the directory exists, another backup process may be running
    echo "Directory $SNAPDIR already exists! Is another backup still running?"
    exit -1
    # Let's make snapshots
# Do the actual backup
# Remove the ZFS snapshot
if [ -d $SNAPDIR ]; then
    echo "$SNAPDIR does not exist!" 1>&2
    exit 2
exit 0

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Multiple accounts on an SSH server: managing key files

I’ve got several domains hosted at the same hosting company, and the company provides SSH access for each of them with a different user name, but with the same SSH server address. As I’m using key-based login to the server (see also my post here) I ran into the following problem: How do I set up my SSH config file such that it knows which key to use for which user name?

It turns out that the solution is easy (thanks Kelvin!): if you use the %r variable in the ~/.ssh/config file it contains the user name which you used when logging in. Similarly, the %h contains the host name you used on the command line. So all I needed to do was to create entries like this:

     IdentityFile ~/.ssh/hosting-%r.key

and make sure that the corresponding key files are named hosting-domain1.key, hosting-domain2.key, etc. and then log in using a command like ssh

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SSH with several keys: fix “Too many authentication failures” error

Yesterday I created an SSH key for a new machine. Today I try to log in to a different machine, one that actually doesn’t use keys, and I got the error mentioned in the title. It turns out SSH offers all available keys by default, so I ran out of login attempts before I noticed it.

The solution is simple: Add

IdentitiesOnly yes

to your ~/.ssh/config file.

A more detailed explanation can be found here.

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Enabling external commands in the Nagios web interface

After an upgrade of one of my Ubuntu server that runs Nagios, I ran into the following error message (again…) when I tried to issue a command from the web interface:

Error: Could not stat() command file ‘/var/lib/nagios3/rw/nagios.cmd’!

This post by Barry O’Donovan shows very nicely how this problem can/should be fixed in Ubuntu. Much cleaner than chmod/chown-ing the directories myself. Thanks Barry!

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Fixing problems after giving your Samba server a new IP address

While moving my DHCP server to a Raspberry Pi I also changed some of the IPs handed out to my (virtual) servers. This lead to problems when I logged into Windows (which is tied to my Samba domain), Windows complained that my roaming profile wasn’t completely synced and browsing network shares didn’t work, copying from (mounted) network shares didn’t work, etc.

In the Samba log files I noticed some references to the old IP address (, e.g.:

[2014/03/13 16:22:23,  0] nmbd/nmbd_become_dmb.c:237(become_domain_master_query_success)
  There is already a domain master browser at IP for workgroup SENW registered on subnet UNICAST_SUBNET.


  [2014/03/13 16:20:07,  0] nmbd/nmbd_browsesync.c:248(domain_master_node_status_fail)
  Doing a node status request to the domain master browser
  for workgroup SENW at IP failed.
  Cannot sync browser lists.

Even after restarting smbd and nmbd, and checking my smb.conf thoroughly, these kept showing up.

It turns out (thanks a lot Matt Godbolt) that nmbd keeps caches in two files (paths as they are on my Ubuntu 12.04 server):

  • /var/cache/samba/browse.dat
  • /var/lib/samba/wins.dat

Simply stop nmbd, delete them, restart nmbd and you’re happy.

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Permantly ban an IP address with fail2ban

Over the last few days I noticed in my logwatch e-mails that one IP address kept trying to log in to my server, even though it was blocked regularly by fail2ban.

Here’s a post that explains how to simply add a list of IP addresses to block permanently. There’s only one catch: the listing provided there contains an error, the word <name> is missing in the iptables command, probably due to HTML conversion. This is the correct line to be insterted into the actionstart section of /etc/fail2ban/action.d/iptables-multiport.conf:

cat /etc/fail2ban/ip.blacklist | while read IP; do iptables -I fail2ban-<name> 1 -s $IP -j DROP; done

Use the following command to check if the IP address is indeed banned:

$ sudo iptables  -L fail2ban-ssh
Chain fail2ban-ssh (1 references)
target     prot opt source               destination         
DROP       all  --        anywhere            
RETURN     all  --  anywhere             anywhere 

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Showing other users (from LDAP) in the LightDM greeter

Ubuntu Linux uses the LightDM greeter (the login screen you see after booting). Since I’m using an LDAP server to store my user accounts and LightDM by default only shows local users I needed to tell LightDM to give me an ‘other user’ option where I can enter a user name and password (I first checked to see if my LDAP connection work by logging in with an LDAP user from the console (tty1).
LightDM is configured in /etc/lightdm/lightdm.conf, but also provides command line tools to set the options. To show the ‘other user’ use:

sudo /usr/lib/lightdm/lightdm-set-defaults --show-manual-login true

This will disable the user list. It adds the line


to the lightdm.conf file.
If you only want to see the “Other” entry run:

sudo /usr/lib/lightdm/lightdm-set-defaults --hide-users true

And lastly you can turn off guest:

sudo /usr/lib/lightdm/lightdm-set-defaults --allow-guest false

Thanks to mfish at!

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Solving “RTNETLINK answers: File exists” when running ifup

On a server with multiple network cards I tried to configure the eth3 interface by editing /etc/network/interfaces (this was an Ubuntu 12.04 machine).

This was the contents of /etc/networking/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address xxx.yyy.zzz.mmm
        gateway xxx.yyy.zzz.1
        dns-nameservers xxx.yyy.zzz.bbb

auto eth3
iface eth3 inet static

When I tried to bring the interface up I got an error message:

$ ifup eth3
RTNETLINK answers: File exists
Failed to bring up eth3.

It took me a while to figure it out, but the problem was the gw line in the eth3 entry. Of course you can only have one default gateway in your setup. I missed this because I was also trying to add routes to networks behind the machine on the other end of eth3.
In the end, removing the gw line in the eth3 entry solved the problem.

My final /etc/networking/interfaces looks like this:

# The loopback network interface
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address xxx.yyy.zzz.mmm
        gateway xxx.yyy.zzz.1
        dns-nameservers xxx.yyy.zzz.bbb

auto eth3
iface eth3 inet static
        post-up /sbin/route add -net netmask gw
        post-up /sbin/route add -net netmask gw
        post-up /sbin/route add -net netmask gw
        post-down /sbin/route del -net netmask
        post-down /sbin/route del -net netmask
        post-down /sbin/route del -net netmask

Update 2013-08-19: Removed network entries as per Ville’s suggestion.

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Installing Loggerhead behind Apache on Ubuntu 11.04


Loggerhead is a webfrontend for Bazaar (usually abbreviated as bzr) repositories. Bazaar is a so-called distributed version control system. So, if you have one or more bzr repositories you can use Loggerhead to look at the files, read the change logs and see the differences between revisions from within your web browser.

The main purpose of this post is to document the steps needed to configure Loggerhead and Apache to work together to publish your bzr repos on the web. The need for this post arose when I tried to get this setup to work and found that there isn’t a lot of documentation on how to get this done and most of it is out of date. The folowing steps were performed on a Linux server with Ubuntu 11.04 installed.

Basic Loggerhead configuration

First, let’s install Loggerhead:

$ aptitude install loggerhead

Although the package is called loggerhead, the actual binary that is run is called serve-branches. The package provides start and stop scripts for the service (/etc/init.d/loggerhead), but to start successfully the file /etc/serve-branches.conf needs to exist. Older documentation I found on the web refers to the file /etc/loggerhead.conf, but that file has become obsolete.

The serve-branches.conf file contains three lines:


Here, the line served_branches points to the directory under which you store your bzr repositories. Each repo needs to be stored in its own directory. So in this example all the repos are in subdirectories of /home/bzr/.

You have to make sure that loggerhead can read the files in that directory. Loggerhead runs as the loggerhead user but I made the directories readable and accessible by all users:

$ chmod -R a+rx /home/bzr/

If you now start Loggerhead:

$ service start loggerhead

you should be able to visit http://localhost:8080 in your browser and see your repositories.
NOTE for Ubuntu 12.04 and 12.10: There seems to be a bug in Loggerhead for these Ubuntu releases (see the link to the Launchpad bug report at the end of this post). In order to start the Loggerhead daemon correctly in these Ubuntu releases the file /etc/init.d/loggerhead must be edited. The line

start-stop-daemon -p $PIDFILE -S --startas /usr/bin/serve-branches --chuid loggerhead --make-pidfile --background --chdir $served_branches -- --prefix=$prefix --port=$port --host=$host --log-folder /var/log/loggerhead 2>/dev/null

must be changed to

start-stop-daemon -p $PIDFILE -S --startas /usr/bin/serve-branches --chuid loggerhead --make-pidfile --background -- file://$served_branches --prefix=$prefix --port=$port --log-folder /var/log/loggerhead 2>/dev/null

Once this is done run restart the Loggerhead service as stated above and it should work again (if you run Loggerhead behind an Apache webserver as detailed below, don’t forget to restart Apache also).

How to publish your branch to this shared repository?

Now that our repository browser is set up, how do we publish our branches to it so that there actually is something to browse through? Here is how you publish your branch to the server, assuming that you are in a directory that contains a branch and want to publish it as myTests:

$ bzr push --create-prefix s

As you probably suspected, the --create-prefix option is only necessary the first time you push your branch. Note that we are using sftp here. Loggerhead itself doesn’t allow writes to the published repos. So, every user that want to push his/her changes to this repository needs to have sftp access to the /home/bzr directory. I solved that problem by adding all people that need to be able to push changes to a Linux group called vcs (for Version Control Systems) and then set the primary group of /home/bzr/ to vcs as well as giving group write permissions to this directory:

$ ls -ld /home/bzr/
drwxrwxr-x 4 root vcs 4096 2011-08-16 23:10 /home/bzr/

Adding Apache to the mix

In my case I already have a web server (Apache) running on port 80. Since I’d rather not open yet another port (8080 in this case) on my router, I wanted to use Apache to hand over the requests for bzr page to Loggerhead. For that I needed to install the following packages:

$ aptitude install python-pastedeploy

Next, I needed to change the contents of the /etc/serve-branches.conf file to this:


The prefix indicates the location in the URL where Apache will serve the repos. In this case that will be

And finally I needed to configure Apache. First, make sure that the proxy and proxy-http modules are loaded:

$ a2enmod proxy proxy_http

Next, create a file /etc/apache/conf.d/sites-available/loggerhead with the following contents:

# Configuration for browsing of Bazaar repos. Make sure loggerhead is running.
<Location "/bzr/">

Note that Loggerhead and Apache run on the same host, that’s why I set the IP to

Finally it’s time to enable the site and restart Apache:

$ a2ensite loggerhead
$ service apache2 restart

Now it should be possible to browse your repos at Note the final /, it’s important.

Securing access with an LDAP connection

I have stored all my Unix user and group information in an LDAP server. To make sure that only people in the Unix group vcs are allowed access to the loggerhead pages, change the Apache configuration file loggerhead to the following:

# Configuration for browsing of Bazaar repos. Make sure loggerhead is running.
<Location "/bzr/">
    # LDAP authentication
    AuthType Basic
    AuthName " VCS users"
    AuthBasicProvider ldap
    AuthLDAPURL "ldap://,dc=yourdomain,dc=com?uid"
    AuthLDAPGroupAttribute memberUid
    AuthLDAPGroupAttributeIsDN off
    Order Allow,Deny
    Allow From All
    Require ldap-group cn=vcs,ou=Groups,dc=yourdomain,dc=com

Lines 11 and 12 are needed because the vcs group is not an LDAP group. I store my Unix (POSIX) groups in a separate OU in the LDAP tree (see line 15).
Don’t forget to restart Apache after making these changes.


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