Category: Linux

Problem:

You want to download an apt source package using

apt-get source <package name>

but instead you see this error message:

E: You must put some 'source' URIs in your sources.list

Solution:

In most cases, you can fix this easily using

sudo apt-get update

If this does not fix the issue, edit /etc/apt/sources.list, e.g. using

sudo nano /etc/apt/sources.list

and ensure that the deb-src lines are not commented out.

Example: You need to change

deb http://archive.ubuntu.com/ubuntu artful main restricted
# deb-src http://archive.ubuntu.com/ubuntu artful main restricted

to

deb http://archive.ubuntu.com/ubuntu artful main restricted
deb-src http://archive.ubuntu.com/ubuntu artful main restricted

Problem:

You want to launch some lxd container using lxc launch […] but instead you get the following error message:

Failed container creation: No storage pool found. Please create a new storage pool.

Solution:

You need to initialize lxd before using it:

lxd init

When it asks you about the backend

Name of the storage backend to use (btrfs, dir, lvm) [default=btrfs]:

choosing the default option (btrfs) means that you’ll have to use a dedicated block device (or a dedicated preallocated file image) for storage. While this is more efficient if you run many containers at a time, I recommend to choose the dir backend for the default storage pool, because that option will be easiest to configure and will not occupy as much space on your hard drive.

See Storage management in lxd for more more details, including different options for storage pools in case you need a more advanced setup.

Warning: If you run fdisk on the wrong drive here or there is some important data left, you might lose all your data and it will be very hard to restore. Before running these commands, triple-check that you’ve used the correct device (e.g. /dev/sdh)!

In order to create a partition table on a device (e.g. /dev/sdh – /dev/sdh1 is not a device but a partition, so using that does not make any sense!), run these commands

sudo fdisk <device file>

If the device doesn’t have a valid partition table, fdisk will automatically create a partition table (but not write it to the disk yet). It will show this output if that is the case (the identifier is random and different every time):

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0x81ee11ff.

Command (m for help):

If you are sure that you want to run the partition, enter w and press return to write the partition table to disk & exit.

The partition table will be effective immediately, but will not contain any partition. In order to create a partition (for this example we will create one partition being as large as the entire device), run

sudo fdisk <device file>

again.

This time, enter the n command (new partition). When it asks you about the partition type and its size, just press return every time to select the defaults. It should look like this (<return> added to show you where you should press return).

Command (m for help): n
Partition type
p primary (0 primary, 0 extended, 4 free)
e extended (container for logical partitions)
Select (default p): <return>
Partition number (1-4, default 1): <return>
First sector (2048-31143935, default 2048): <return>
Last sector, +sectors or +size{K,M,G,T,P} (2048-31143935, default 31143935): <return>

After that, when fdisk prompts for a command again (i.e. when it says Command (m for help): ), enter w in order to write the changes (i.e. the new partition) to the disk & exit. After fdisk exits, you can see the partition in /dev, e.g. /dev/sdh1

After that, you’ll likely need to create a filesystem on that partition, e.g. sudo mkfs.ext4 /dev/sdh1 or sudo mkfs.vfat /dev/sdh1 . Make sure to create the correct filesystem for the operating system and usecase the device will be used in.

This error is caused by an expired GPG key that is used in the MongoDB repository.

This key has already been renewed, but you need to tell GPG to update it. Run:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 0C49F3730359A14518585931BC711F9BA15703C6

For more details, see this GitHub post.

If you edited some nginx config file and nginx doesn’t want to reload or restart, e.g. with an error message like this:

# service nginx reload
Job for nginx.service failed because the control process exited with error code.
See "systemctl  status nginx.service" and "journalctl  -xe" for details.

you likely have some error in one of your config files.

There’s a simple command to check for errors (you need to run it as root): nginx -t

Example output:

nginx: [emerg] unknown directive "autoindex$" in /etc/nginx/sites-enabled/mysite:31
nginx: configuration file /etc/nginx/nginx.conf test failed

Firstly, the last line tells you that there actually is some error in the config files.
The first line tells you exactly where it is: /etc/nginx/sites-enabled/mysite:31 means: Look in the file /etc/nginx/sites-enabled/mysite, line 31.

In this particular case, the actual error message is unknown directive "autoindex$". By checking the aforementioned file I was able to find out that I accidentally entered autoindex $; instead of autoindex on;

After fixing this issue, nginx -t shows that the configuration file seems correct now:

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

Note that while most cases of nginx failing to (re)start are caused by issues in the config files, there are some cases in which the config file seems correct and nginx will still not start up. In that case. have a look at the logfile which is commonly located at /var/log/nginx/error.log . You need to be root in order to view it. I recommend this command:

sudo tail -n 1000 /var/log/nginx/error.log

Just press Ctrl+X. If you dont have unsaved changes, this will exit nano immediately.

In case you have unsaved changes, it will ask you whether to save those changes after pressing.

• Press Y to tell it to save the changes you’ve made. It will then ask you to check or enter the filename to save to. Once you are finished with the filename, press Enter.
• Press N to discard all changes (you won’t be able to restore your changes later) and exit nano immediately.

baloo is a KDE desktop search component that indexes files in order to speed up the search.

The index can get quite large, e.g. my index consumes more than 2 GB of HDD space:

$ balooctl indexSize
Actual Size: 2,04 GiB
Expected Size: 1,33 GiB

           PostingDB:     313,32 MiB    22.924 %
         PosistionDB:     521,05 MiB    38.122 %
            DocTerms:     167,93 MiB    12.287 %
    DocFilenameTerms:      53,46 MiB     3.912 %
       DocXattrTerms:            0 B     0.000 %
              IdTree:       9,79 MiB     0.716 %
          IdFileName:      41,71 MiB     3.052 %
             DocTime:      25,80 MiB     1.887 %
             DocData:       2,02 MiB     0.148 %
   ContentIndexingDB:      14,86 MiB     1.087 %
         FailedIdsDB:            0 B     0.000 %
             MTimeDB:       9,12 MiB     0.667 %

If you don’t want to use baloo anyway or if you just want to re-index all files, you might want to delete the entire index:

rm -rf ~/.local/share/baloo

Note that if you haven’t disabled baloo using balooctl stop ; balooctl disable it might silently re-create the index in the background.

Problem:

You’ve uploaded a DEB package to a Launchpad PPA (e.g. using dput), but you get an error message similar to this:

Solution:

You need to use a proper email address (which must be registered in Launchpad) in debian/changelog .

In order to do this, set the $DEBEMAIL environment variable before running dch

Example:

export DEBEMAIL=myemail@example.com
dch [...]

If $DEBEMAIL is not set, [username]@[hostname] will be used

Problem:

You are trying to run a docker container or do the docker tutorial, but you only get an error message like this:

docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.26/containers/create: dial unix /var/run/docker.sock: connect: permission denied.
See 'docker run --help'.

 Solution:

The error message tells you that your current user can’t access the docker engine, because you’re lacking permissions to access the unix socket to communicate with the engine.

As a temporary solution, you can use sudo to run the failed command as root.
However it is recommended to fix the issue by adding the current user to the docker group:

Run this command in your favourite shell and then completely log out of your account and log back in (if in doubt, reboot!):

sudo usermod -a -G docker $USER

After doing that, you should be able to run the command without any issues. Run docker run hello-world as a normal user in order to check if it works. Reboot if the issue still persists.

Logging out and logging back in is required because the group change will not have an effect unless your session is closed.

When running smartctl on your hard drive, you often get a plethora of information that can be hard to interpret for unexperienced users. This post attempts to provide aid in interpreting what the technical reasons behind the error messages are. If you’re looking for advice on whether to replace your hard drive, the only guidance I can give you is it might fail any time, so better backup your data, but it might also run for many years to come.. Furthermore, this article does not describe basic SMART WHEN_FAILED checking but rather interpretation of more subtle signs of possibly impending HDD failures.

Read more

A few days ago, Let’s Encrypt into public beta. At the time of writing this article, almost 120k certificateshave been issued, including the certificate for TechOverflow.

I really like the Let’s Encrypt service and I believe it might actually change the way people perceive HTTPS encryption. However, there is one rarely-mentioned side-effect when protecting your domains with their certificates.

Let’s Encrypt publishes certificate transparency logs at crt.sh. This transparency does not come without side-effects, however: crt.sh effectively publishes.

In other words, hiding sites from the public by not publishing their (sub-)domain names anywhere will not work when you issue a certificate for the domain on services like Let’s Encrypt.

Read more

Problem:

You have an nginx host that is configured as reverse-proxy-only like this:

server {
    server_name  my.domain;
    [...]
    location / {
        proxy_pass http://localhost:1234;
    }
}

For this host, you want to use Let’s Encrypt to automatically issue a certificate using the webroot method like this:

certbot certonly -a webroot --webroot-path ??? -d my.domain

The reverse-proxied webserver does not provide a webroot to use for the automated autentication process and you want to keep the flexibility of updating the cert at any time without manually modifying the nginx configuration.

Read more

After upgrading my server from Debian Wheezy to Jessie, I encountered the following error during apt-get update:

/usr/lib/apt/methods/https: symbol lookup error: /usr/lib/x86_64-linux-gnu/libhogweed.so.2: undefined symbol: __gmpn_cnd_add_n

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Problem:

You want to query the current resolution of a screen connected as framebuffer device (e.g. /dev/fb0). Read more

Symptomatics:

I have both the Toshiba Z830 and R850 for a couple of years now. On both, I’m using the current LTS versions of KUbuntu (at the time of writing this, 14.04). Although, I’m absolutely satisfied with them, there’s a little issue regarding the backlight:

On startup, the backlight works perfectly well. I can change the settings using FN+F6/F7 without any issues. However, after putting the device into standby and waking it up again, pressing said hotkeys shows the backlight percentage dialog, but does not change the brightness.

Because Ubuntu’s SSD reboots are pretty fast Iimply didn’t care about the issue for the past few years. However, out of curiosity, I successfully fixed the issue today.

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Problem:

You use saltstack to automatically deploy configuration to your servers. After installing nginx with the default config, you need to increase the server_names_hash_bucket_size because it won’t startup otherwise.

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