Category: Ubuntu Server

I’m run into some error message like:  “Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column”.  It’s turns out that this is caused by MySQL updating the way it behave in relation to aggregate functions since MySQL 5.7.  Here is how I solved it on Ubuntu .

You can find out what mode your MySQL server is running:

SELECT @@GLOBAL.sql_mode;

My Ubuntu 19.10 got this:

ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

Then take this and delete “ONLY_FULL_GROUP_BY”.  You can then add this to MySQL configuration file.    On my Ubuntu there is a file located at /etc/mysql/my.cnf and inside here is specifies two folders where you could put the configuration:

!includedir /etc/mysql/conf.d/
!includedir /etc/mysql/mysql.conf.d/

I have edited /etc/mysql/conf.d/mysql.cnf and put in

[mysqld]
sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

 

If you are trying get sar working you might get this error message: “Cannot open /var/log/sysstat/sa08: No such file or directory”.  Essentially, you need to enable data collection. You do this by editing /etc/default/sysstat

nano /etc/default/sysstat

Then change:

ENABLED=”false” to ENABLED=”true”

Hope this helps someone.

I just tried to install the htpasswd command and got the following error:  Unable to locate package htpasswd. Turns out you need apache2-utils:

<code>sudo apt-get install apache2-utils</code>

Sometimes it can be really useful to give a user privileges to run a specific command as root. For example – if you wanted to allow a user to restart a specific service or run a specific program as root without given them access to the whole server. You can configure this using visudo command as root. Note: you really must be root when you do this and not a sudo.

 sudo su -

Then..

visudo

You can then modify the configuration file. There are specific sections in the config file which are show below. For example – I want to give a user called debug permission to run supervisorctl as root.

....

# User alias specification
debug ALL=(ALL) NOPASSWD:/usr/bin/supervisorctl

Hope this is helpful.

I wanted to monitor the bandwidth usage on my Ubuntu server without a full blown graphic monitoring system but something that I could just check once in a while just to see how things are running. I found an really simple tool called vnstat. It’s good because it’s simple, fast and easy to use and that doesn’t require a PhD in networking to get going. It also nicely presents the data with good summaries.

Here is how I setup network traffic monitoring using vmstat:

1 – Install vnstat – note there is another program called vmstat – so be careful what you type.

sudo apt-get install vnstat

2 – Configure the network adapter to monitor. Vnstat automatically configures the network adapters however it’s worth checking that they are correct and having a quick peek through the configuration file.

sudo nano /etc/vnstat.conf

If you do have made any change then don’t forget to restart the service.

sudo service vnstat restart

3 – Get you first report – You will have to wait a few minutes to get your first report. This how a typical report looks like:

#vnstat

outputs:

Database updated: Sun Nov  9 20:11:55 2014

   eth0 since 07/22/14

          rx:  4.56 GiB      tx:  109.97 GiB      total:  114.53 GiB

   monthly
                     rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
       Oct '14      1.24 GiB |   38.39 GiB |   39.63 GiB |  124.13 kbit/s
       Nov '14    361.70 MiB |    9.56 GiB |    9.91 GiB |  108.84 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated      1.20 GiB |   32.43 GiB |   33.62 GiB |

   daily
                     rx      |     tx      |    total    |   avg. rate
     ------------------------+-------------+-------------+---------------
     yesterday     37.62 MiB |  805.67 MiB |  843.29 MiB |   79.96 kbit/s
         today     29.32 MiB |  176.40 MiB |  205.73 MiB |   23.18 kbit/s
     ------------------------+-------------+-------------+---------------
     estimated        34 MiB |     209 MiB |     243 MiB |

Hope this is useful to someone. Let’s me know if you have any improvements to this post or can recommend other tools that readers of this blog might be interested in.

The sudo command checks the permission of the /etc/sudoers file and also the contents of /etc/sudoers.d/ before allowing you to use the sudo command.

For example you might be warned:

sudo: /etc/sudoers is mode 0777, but should be 0440

or perhaps:

sudo: can't open /etc/sudoers: permission denied.
sudo: no valid sudoers sources foundm quitting

Therefore, if you don’t have root login (which is generally good security practise) then you might not be able to change the permission back without dropping into recovery mode.

1 – Reboot the machine

2 – Select boot from recovery more

3 – fsck the disk which will then mount the disks as read/write

4 – Drop to root shell

5 – chmod 0400 /etc/sudoers

6 – reboot the machine and you are fixed