Debian now packages MariaDB, so this is, unfortunately not up-to-date anymore.
The basic principles should also apply to MariaDB.
So, my system sometimes takes some time to boot. After systemd-analyze
critical-path I saw that mainly my local MySQL server is to blame here.
After researching how to use socket activation with MySQL, I only found
IP-based socket activation. So I dug a little bit deeper
and now would like to present my way to my solution.
Final Solution at the end of the page
I started out by simply trying to adapt the IP-based socket activation to
Unix sockets:
# /etc/systemd/system/proxy-to-mysql.socket
[Socket]
ListenSocket=/var/run/mysqld/mysqld.sock
[Install]
WantedBy=sockets.target
# /etc/mysql/mysql.conf.d/mysql.cnf
# [...]
[mysql_safe]
socket = /var/run/mysqld/mysqld.real.sock
#[...]
[mysqld]
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.real.sock
#[...]
# /etc/systemd/system/proxy-to-mysql.service
[Unit]
Requires=mysql.service
Ater=mysql.service
[Service]
ExecStart=/lib/systemd/systemd-socket-proxyd /var/run/mysqld/mysqld.real.sock
PrivateTmp=no
PrivateNetwork=no
Stopping MySQL and verifying the Unit status:
sudo systemctl stop mysql
sudo systemctl start proxy-to-mysql.socket
systemctl status proxy-to-mysql.{socket,service} mysql
# proxy-to-mysql.socket is active
# proxy-to-mysql.service is inactive
# mysql is inactive
But when I now try to connect to MySQL, it simply hangs… looks like the
proxied socket does not answer. Checking the runtime directory
/var/run/mysqld, there is no mysqld.real.sock!
mysql
# hangs here...
# ^C
ls /var/run/mysql
# mysqld.sock
# (No mysqld.real.sock!)
Looking into the MySQL server error log /var/log/mysql/error.log, there is an
“Permission Denied” error while creating the socket. Checking the permissions of
/var/run/mysqld, owner of the directory is root:root:
ls -ld /var/run/mysqld
# total 0
# drwxr-xr-x 2 root root 60 Jan 19 12:41 .
# drwxr-xr-x 43 root root 1340 Jan 19 12:46 ..
# srw-rw-rw- 1 root root 0 Jan 19 12:41 mysqld.sock
Seems like the proxy-to-mysql.socket is not correctly configured. After some
more reasearch I found SockerUser and SocketGroup and added them with user
and group mysql to the Socket, but that only made the socket itself owned by
mysql:mysql, not the directory, so that didn’t help.
I then decided to move the mysqld.real.sock to it’s own directory,
/var/run/mysqld.real/mysqld.sock:
# /etc/mysql/mysql.conf.d/mysql.cnf
# [...]
[mysql_safe]
socket = /var/run/mysqld.real/mysqld.sock
#[...]
[mysqld]
pid-file = /var/run/mysqld.real/mysqld.pid
socket = /var/run/mysqld.real/mysqld.sock
#[...]
# /etc/systemd/system/proxy-to-mysql.service
[Unit]
Requires=mysql.service
Ater=mysql.service
[Service]
ExecStart=/lib/systemd/systemd-socket-proxyd /var/run/mysqld.real/mysqld.sock
PrivateTmp=no
PrivateNetwork=no
Applying changes…
sudo systemctl daemon-reload
sudo systemctl stop mysql proxy-to-mysql.service
sudo systemctl restart proxy-to-mysql.socket
And another try.
Same error, again “Permission denied”, this time /var/run is the problem,
which again is owned by root:root. Looking into the
/lib/systemd/system/mysql.service, I see RuntimeDirectory=mysqld. After some
more resarch I found out that this tells systemd to create the /var/run/mysqld
directory. I now want to change that to RuntimeDirectory=mysqld.real. Directly
changing the service file in /lib is not a good idea, with the next mysql
package update my changes would be overwritten. Fortunately there is systemctl
edit to the rescue, so I use that to overwrite the RuntimeDirectory:
sudo systemctl edit mysql
[Service]
# We need to clear first, otherwise it would extend the variable to a value of
# "mysqld mysqld.real"
RuntimeDirectory=
RuntimeDirectory=mysqld.real
systemctl edit reloads the daemon for us, so we don’t need to do it manually.
Another try, this time directly the mysql service.
sudo systemctl start mysql
# Takes some time, finally fails.
Still “Permission denied”.
Some thinking…
AppArmor!
And yes, there is a /etc/apparmor.d/usr.sbin.mysql profile, which only allows
mysql to write to /var/run/mysqld! Again the issue with not being able to
directly edit the file due to overwrites by updates. Fortunately there is
/etc/apparmor.d/local/ for extensions. :)
# /etc/apparmor.d/local/usr.sbin.mysqld
/var/run/mysqld.real/mysqld.pid rw,
/var/run/mysqld.real/mysqld.sock rw,
/run/mysqld.real/mysqld.pid rw,
/run/mysqld.real/mysqld.sock rw,
(/var/run is a symlink to /run).
Another try!
sudo systemctl start mysql
I now realize how long it takes to start the mysql service. Looking into the
error log, there is no error, mysqld seems to be running fine. Checking via
mysql --socket /var/run/mysqld.real/mysqld.sock verifes: I can connect to
mysql through that socket! :)
So I got to htop to kill the systemctl start and see a child process
mysqladmin ping. Trying that command myself, it does not work. Some
thinking… Ah, yes! there is an After=mysql in the proxy-to-mysqld.service,
so the systemd-socket-proxyd won’t start until the mysql.service is running,
which means /var/run/mysqld/mysqld.sock is still dead.
But why is this mysqladmin ping running anyway? I remember that there was a
process between the mysqladmin ping and the systemctl start mysql, a
mysql-systemd-start post. And that one I remember I saw in the
mysql.service. Looking into the mysql.service again, there is
ExecStartPost=/usr/share/mysql/mysql-systemd-start post. Looking into the file
the post case executes mysqladmin ping in a loop, I guess to ensure mysqld
is really up.
The Problem here is that by default this uses the /var/run/mysqld/mysqld.sock,
which is still dead while the command runs. Adjusting the command directly in
the file again is not a good idea, so I copied it to /etc/mysql, added
--socket /var/run/mysqld.real/mysqld.sock and changed the ExecPostStart to
use that file.
# /etc/mysql/mysql-systemd-start, copied from
# /usr/share/mysql/mysql-systemd-start
# [...]
pinger () {
server_up=false
for i in $(seq 1 30); do
sleep 1
if mysqladmin -S /run/mysqld.real/mysqld.sock ping >/dev/null 2>&1; then
# [...]
sudo systemctl edit mysql
[Service]
# Clear var so we don't extend it
ExecPostStart=
ExecPostStart=/etc/mysql/mysql-systemd-start post
And another try!
sudo systemctl stop mysql proxy-to-mysql.{socket,service}
sudo systemctl start proxy-to-mysql.socket
sudo systemctl start mysql
# Success, works!
sudo systemctl stop mysql
mysql
# mysql>
# Yeah! Also works!
Finally!
Now just one problem remains: The mysql.service link in
/etc/systemd/system/multi-user.target/mysql.service, which would result in
mysql still starting on boot. I can remove this link, but it will come back, as
there is WantedBy=multi-user.target in the Install section of the
mysql.service. Unfortunately this cannot be overwritten using a systemctl
edit mysql override config. One has to copy the full service file to
/etc/systemd/system and change the values there. But, okay, I can live with
that for the moment. systemd still helps one with that: sudo systemctl edit
--full mysql.service. I just removed the [Install] section.
Summary
All the changed and create files are summarized below.
You can find the created files also in this Git repo:
https://git.joinout.de/mysql-socket-activation
Proxy Socket and Service
/etc/systemd/system/proxy-to-mysql.socket
[Socket]
ListenSocket=/var/run/mysqld/mysqld.sock
[Install]
WantedBy=sockets.target
/etc/systemd/system/proxy-to-mysql.service
[Unit]
Requires=mysql.service
After=mysql.service
[Service]
ExecStart=/lib/systemd/systemd-socket-proxyd /var/run/mysqld/mysqld.real.sock
PrivateTmp=no
PrivateNetwork=no
MySQL Server configuration
/etc/mysql/mysql.conf.d/mysql.cnf
# [...]
[mysql_safe]
socket = /var/run/mysqld.real/mysqld.sock
#[...]
[mysqld]
pid-file = /var/run/mysqld.real/mysqld.pid
socket = /var/run/mysqld.real/mysqld.sock
#[...]
/etc/apparmor.d/local/usr.sbin.mysqld
/var/run/mysqld.real/mysqld.pid rw,
/var/run/mysqld.real/mysqld.sock rw,
/run/mysqld.real/mysqld.pid rw,
/run/mysqld.real/mysqld.sock rw,
MySQL Service adjustments
/etc/mysql/mysql-systemd-start
(Copied from /usr/share/mysql/mysql-systemd-start and added --socket
/var/run/mysqld.real/mysqld.sock to the mysqladmin command)
# [...]
pinger () {
server_up=false
for i in $(seq 1 30); do
sleep 1
if mysqladmin --socket /run/mysqld.real/mysqld.sock ping >/dev/null 2>&1; then
# [...]
/etc/systemd/system/mysql.service.d/override.conf
[Service]
ExecStartPost=
ExecStartPost=/etc/mysql/mysql-systemd-start post
RuntimeDirectory=
RuntimeDirectory=mysqld.real
/etc/systemd/system/mysql.service
sudo systemctl edit --full mysql.service
# remove the [Install] section
