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Interesting links: October 4th 2015

Here's a bunch of links I found interesting in the last few weeks:

Batch create new users on Linux

A while ago I had to create many new users on a Linux machine. Since I'm lazy, I opted to automate this process. The newusers command combined with pwgen (to generate new passwords) was the solution.

First I installed pwgen, a utility to automatically generate passwords:

$ sudo apt-get install pwgen

I created a file with the new user names to create.

$ cat newusers.txt

A simple shell one-liner generates a new file from this in the right format for the newusers tool:

$ for USER in $(cat newusers.txt); do 
  echo "$USER:$(pwgen 12 -n1)::::/home/$USER:/bin/bash" >> newusers.created.txt;

Finally, we create the new users:

$ sudo newusers newusers.created.txt

The newusers.created.txt file was handed over to the person in charge of notifying the users about their new account.

Auto-mount external USB disk on a server

Althought modern Linux desktops generally automatically mount external USB disks when plugged in, servers usually don't do this. When I replaced my home server desktop model with a Raspberry Pi 2 (running Raspbian), I wanted it to automatically mount USB drives and, more importantly, make the same USB drive available at the same path at all times.

Enter usbmount

The USBmount Debian package automatically mounts USB mass storage devices (typically USB pens) when they are plugged in, and unmounts them when they are removed. The mountpoints (/media/usb[0-7] by default), filesystem types to consider, and mount options are configurable. When multiple devices are plugged in, the first available mountpoint is automatically selected. If the device provides a model name, a symlink /var/run/usbmount/MODELNAME pointing to the mountpoint is automatically created.

Just what I needed.

root@rasp# sudo apt-get install usbmount
# Plug in USB drive
root@rasp# ls -la /var/run/usbmount/
total 0
lrwxrwxrwx 1 root root 11 Oct  4 10:30 Seagate_Expansion_1 -> /media/usb0
lrwxrwxrwx 1 root root 11 Oct  4 10:30 ST4000DM_000-1F2168_1 -> /media/usb1

Great. Now I wanted the "Seagate_Expansion_1" disk to always become available at /storage. I could have created a symlink from /storage to  /var/run/usbmount/Seagate_Expansion_1, but I ran into a problem with SSHfs when trying to mount a server-side symlink on my client machine:

user@client$ sshfs -o transform_symlinks -o follow_symlinks Shares/timmy-storage/ Not a directory

So a symlink was out of the question. The binding option of 'mount' however, worked just fine:

# On the server
root@rasp# rm /storage
root@rasp# mkdir /storage
root@rasp# mount --bind /var/run/usbmount/Seagate_Expansion_1 /storage

# On the client
user@client$ sshfs Shares/timmy-storage/
user@client$ ls -l Shares/timmy-storage
total 72
drwxr-xr-x 1 1002 1003 4096 Sep 17 13:58 apps
drwxr-xr-x 1 root root 4096 Aug 24 09:15 backup

So I modified /etc/usbmount/mount.d/00_create_model_symlink and added the following code:

if [ "$name" = "Seagate_Expansion_1" ]; then
    mount --bind "/var/run/usbmount/$name" /storage

This is not a very clean solution, but it serves its purpose just fine. A nicer implementation would create a new file "01_mount_bind" which reads a config file to determine which model names to mount –bind where. That implementation is left as a reader exercise ;-)

With this setup the /storage path will automatically become available at boot-time or when the correct USB drive is plugged in. I can use SSHfs to mount the remote /storage on my Linux machine. Samba takes care of the Windows users.

Ansible-cmdb v1.6: Support for dynamic inventories (and more)

I've just released ansible-cmdb v1.6. This is a feature release, including the following changes:

Get the new release from the Github released page.

A new Material design for Ansible-cmdb v1.5

Ansible-cmdb takes the output of Ansible's setup module and converts it into a static HTML overview page containing system configuration information.

While the previous generated overview page was functional, it didn't look very good. So for the v1.5 release (which is now available), I gave it an overhaul. I decided on Material design because it gives a modern, clean look and feel. The host overview page now looks like this:




The column toggle buttons are more recognisable as actually being toggles and the table of hosts feels a lot cleaner. The bar at the top stays in view even when scrolling. When viewing a hosts detailed information, the header text changes to the host name, making it easier to recognise which host's information you're looking at:



The header bar also includes a link back to the top of the page. This is a big improvement over the previous design, which lacked such a feature.The new design also works better on smaller screens such as tablets or mobiles, although it could still do better.

Other than the new design, the v1.5 release also works when viewing it locally in the browser, without the need to specify the -p local_js option.

You can view a live example or download the new release from the Github releases page.

More information on ansible-cmdb can be found in the README.



Ansible-cmdb v1.4: a host overview generator for ansible-managed hosts

Ansible-cmdb takes the output of Ansible's setup module and converts it into a static HTML overview page containing system configuration information. It supports multiple templates and extending information gathered by Ansible with custom data.

You can visit the Github repo, or view an example output here.

This is the v1.4 release of ansible-cmdb, which brings a bunch of bug fixes and some new features:

I would like to extend my gratitude to the following contributors:

If you've got any questions, bug reports or whatever, be sure to open a new issue on Github!

Ansible-cmdb v1.3: a host overview generator for ansible-managed hosts

A few days ago I released ansible-cmdb. Ansible-cmdb takes the output of Ansible's setup module and converts it into a static HTML overview page containing system configuration information. It supports multiple templates and extending information gathered by Ansible with custom data.

The tool was positively received and I got lots of good feedback. This has resulted in v1.3 of ansible-cmdb, which you can download from the releases page.

This is a maintenance release that fixes the following issues:

For more information, see the Github page. Many thanks to the bug reporters and contributors!

Introducing ansible-cmdb: a host overview generator for ansible-managed hosts

For those of you that are using Ansible to manage hosts, you may have noticed you can use the setup module to gather facts about the hosts in your inventory:

$ ansible -m setup --tree out/ all
$ ls out
centos.dev.local     eek.electricmonk.nl zoltar.electricmonk.nl
debian.dev.local     jib.electricmonk.nl
$ head out/debian.dev.local 
    "ansible_facts": {
        "ansible_all_ipv4_addresses": [
        "ansible_all_ipv6_addresses": [
        "ansible_architecture": "x86_64", 
        "ansible_bios_date": "12/01/2006",

The setup module in combination with the --tree option produces a directory of JSON files containing facts about ansible-managed hosts such as hostnames, IP addresses, total available and free memory, and much more.

I wrote ansible-cmdb to take that output and generate an user-friendly host overview / CMDB (Configuration Management Database) HTML page. Usage is simple:

$ ansible -m setup --tree out/ all   # generate JSON output facts
$ ansible-cmdb out/ > cmdb.html      # generate host-overview page

Here's an example of what it produces.

And here's a screenshot:


It can read your hosts inventory and gather variable values from it, which can be used in the templates that produce the output. You can also extend the gathered facts easily with your own facts by manually creating or generating additional output directories containing JSON files. This even allows you to manually define hosts which are not managed by Ansible.

Ansible-cmdb is template-driven, which means it's rather easy to modify the output. The output is generated using Mako templates

I've just released v1.2. Packages are available in source, Debian/Ubuntu and Redhat/Centos formats. 

For more information, see the Github page. I hope you like it!

Openvaz: Creating credentials is very slow [FIXED]

When creating new credentials on Openvaz (6, 7 and 8), it takes a very long time to store the credentials.

The problem here is that the credentials are stored encrypted, and Openvaz (probably) has to generate a PGP key. This requires lots of random entropy, which is generally not abundantly available on a virtual machine. The solution is to install haveged:

sudo apt-get install haveged

Haveged will securely seed the random pool which will make a lot of random entropy available, even if you have no keyboard, mouse and soundcard attached. Ideal for VPSes.

SSH ChrootDirectory / sftponly not working [FIXED]

I was trying to setup a jail for SSH on Ubuntu 14.04, but it didn't seem to work. The user I was trying to jail using ChrootDirectory could login with SFTP, but could still see everything. Turns out there were a few issues that were causing this. The summary is:

All paths to the jail must have correct ownerships and permissions

All directories in the path to the jail must be owned by root. So if you configure the jail as:

ChrootDirectory /home/backup/jail

Than /home, /home/backup/ and /home/backup/jail must be owned by root:<usergroup>:

chown root:root /home
chown root:backup /home/backup
chown root:backup /home/backup/jail

Permissions on at least the home directory and the jail directory must not include world-writability or group-writability:

chmod 750 /home/backup
chmod 750 /home/backup/jail

Ubuntu's SSH init script sucks

Ubuntu's SSH init script (both sysv init and upstart) suck. They don't actually even restart SSH (notice the PID):

# netstat -pant | grep LISTEN | grep sshd
tcp   0   0*    LISTEN   13838/sshd     
# /etc/init.d/ssh restart
[root@eek]~# netstat -pant | grep LISTEN | grep sshd
tcp   0   0*    LISTEN   13838/sshd      

The PID never changes! SSH isn't actually being restarted! The bug has been reported here: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1390012

To restart it you should use the "service" command, but even then it might not actually restart:

# service ssh restart
ssh stop/waiting
ssh start/running
[root@eek]~# netstat -pant | grep LISTEN | grep sshd
tcp    0   0*   LISTEN   13838/sshd

This generally happens because you've got an error in your ssh configuration file. Naturally they don't actually bother with telling you as much, and the log file also shows nothing.

The Match section in the SSHd configuration must be placed at the end of the file

When I finally figured out that SSH wasn't being restarted, I tried starting it by hand. You might run into the following error:

# sshd -d
sshd re-exec requires execution with an absolute path

You should execute it with the full path because SSHd will start new sshd processes for each connection, so it needs to know where it lives:

# /usr/sbin/sshd

Now I finally found out the real problem:

# /usr/sbin/sshd
/etc/ssh/sshd_config line 94: Directive 'UsePAM' is not allowed within a Match block

My config looked like this:

Match User obnam
    ChrootDirectory /home/obnam/jail
    X11Forwarding no
    AllowTcpForwarding no
    ForceCommand internal-sftp
UsePAM yes
UseDNS no

Aparently SSH is too stupid to realize the Match section is indented and thinks it runs until the end of the file. The answer here is to move the section to the end of the file:

UsePAM yes
UseDNS no
Match User obnam
    ChrootDirectory /home/obnam/jail
    X11Forwarding no
    AllowTcpForwarding no
    ForceCommand internal-sftp

This will fix the problem and sftponly should work now.