Troubleshoot MySQL

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MySQL's role in FOG

MySQL is used to hold information and metadata about hosts, images, groups, snapins, various web-level fog settings, and other things. It does not house the actual image data. In newer Linux, it's being phased out in favor of MariaDB. All commands for MySQL will work for MariaDB.

Easy & quick MySQL test

For the main server and all storage nodes, you may test to see if there is a proper database connection happening or not by visiting the below URL. Replace the x.x.x.x with the IP address of the system you wish to test, and test each system one by one.


If everything is working, the output will only report the server's FOG version and nothing else. All servers in a distributed FOG system should always be kept on the same version.

Manually Testing MySQL

On your FOG server, you can check passwords and the existence of the FOG database by issuing these commands:

No Password:

mysql -D fog

Test with a username and password (note no space between -p and the password):

mysql -u UserNameHere -pPasswordHere -D fog

For a remote server or from a storage node, use:

mysql -u UserNameHere -pPasswordHere -h X.X.X.X -D fog
  • X.X.X.X represents where you'd put the remote host's IP address.
  • -u is username
  • -p is password
  • -h is host
  • -d is database

MySQL Service

CentOS / RHEL / Fedora

Check status:

systemctl status mysql

Restart service:

systemctl restart mysql

Debian / Ubuntu

Check status:

service mysql status

Restart service:

service mysql restart

MySQL Config File

The location of this file varies based on the distribution of Linux you're using. Usually it's called my.cnf and it's probably best to just issue a search command for the file and then figure out which one of the results it is, generally you can pick it out quickly based on the path that the file is in. Here's how to search:

find / -type f -name my.cnf

Here is a sample output from Fedora 23:


In this case, the first result is the right file, /etc/my.cnf Looking into this particular file (on Fedora 23), there is a line that says !includedir /etc/my.cnf.d This means any files in that directory, /etc/my.cnf.d are included in MySQL's configuration.

MySQL credentials for FOG Main and Storage Nodes

The installer sets up FOG with the MySQL Credentials given during installation. These credentials are then stored inside of /opt/fog/.fogsettings for use with the next installation/update. Fog builds a particular web file, /var/www/html/fog/lib/fog/config.class.php this file's settings are what the FOG web front end uses to access MySQL and other things as well.

If those files have incorrect credentials, then there will be mysql permission and access errors in the Apache error logs, and maybe computers will not be able to boot from the FOG Main server or storage nodes either. bind-address defined inside of the my.cnf file can also cause this.

By default, FOG does not set any MySQL password for the main fog server, but FOG Storage nodes MUST use the fogstorage mysql user (or some remote-enabled user that has permissions to the fog db). Storage Nodes communicate with the main FOG server's MySQL database directly in order to update tasking and to present proper boot.php iPXE scripts to clients. This Username/password is auto-generated during installation and can be found here:

Web Interface -> FOG Configuration -> FOG Settings -> FOG Storage Nodes -> FOG_STORAGENODE_MYSQLPASS and FOG_STORAGENODE_MYSQLUSER

From a FOG Storage node, you may try this username & password combination using the example above in the testing section.

See also: Password Central

Reset MySQL fog user and password

DROP USER 'fog'@'localhost';

#Create the user using a password:
CREATE USER 'fog'@'localhost' IDENTIFIED BY 'YourPasswordGoesHere';

#Create the user without a password:
CREATE USER 'fog'@'localhost';

GRANT ALL ON fog.* TO 'fog'@'localhost';

Newer MySql and Ubuntu 16+ method:

ALTER USER 'fog'@'localhost' IDENTIFIED WITH mysql_native_password BY 'YourPasswordGoesHere';
ALTER USER 'fog'@'' IDENTIFIED WITH mysql_native_password BY 'YourPasswordGoesHere';
#Or no password:
ALTER USER 'fog'@'localhost' IDENTIFIED WITH mysql_native_password BY '';

Change MySQL user's password

You can change a user's password and where they are able to connect from with this command:

#Enable only local access:
SET PASSWORD FOR 'fogstorage'@'localhost' = PASSWORD('PasswordHere');

#Enable access from remotely:
SET PASSWORD FOR 'fogstorage'@'%' = PASSWORD('PasswordHere');

Manually export / import Fog database

Related article: Migrate FOG


mysqldump -u USERNAME -pPASSWORD -h HOSTNAME fog > fogDB.sql


mysql -u USERNAME -pPASSWORD -h HOSTNAME fog < fogDB.sql

Example using root and 13375p3@k as the password on the local host.

#Exporting my DB locally on my FOG server...
mysql -u root -p13375p3@k fog > fog_backup.sql

#Here is an import example...
mysql -u root -p13375p3@k fog < fog_backup.sql

#Here is an example of exporting a remote DB to your current directory, 
#where x.x.x.x would be replaced by the IP of the remote system...

mysql -u root -p13375p3@k -h x.x.x.x fog > fog_backup.sql

Enable remote mysql access

Generally this isn't needed, as a "fogstorage" user is already setup with remote access for storage node purposes by the FOG Installer (In 1.3.0). However if you wanted ease of interaction to do testing or development on the FOG database via remote access with a third party tool (such as HeidiSQL), then you'd need to enable remote access on an account, or make a new account and enable remote access for it.

SET PASSWORD FOR 'fogstorage'@'%' = PASSWORD('PasswordHere');

If you want to restrict access to a specific IP, replace the percent symbol (%) with an IP.

Some systems have a bind address set. You can disable that in the my.cnf file. Search for that file with this:

find / | grep /my.cnf

Comment out these lines with a hash tag #

#bind-address =

Increase maximum simultaneous MySQL connections

If you're imaging 50 to 200 computers simultaneously, or simply have a very large amount of hosts, you'll find the below settings helpful.

SET GLOBAL max_connections = 200;
flush hosts;

Open the my.cnf file and make the below change.

Fedora 20,21,22:


Ubuntu 14:


max_connections = 200

then restart mysql

Repair broken database

If you've filled the partition that contains the MySQL Database file completely full, it's highly likely that your MySQL database is now corrupted (and probably several other things too if your really unlucky). You can check for issues and attempt to repair them like this:

mysqlcheck -r fog

If you're able to successfully repair the database, promptly do a DB export via the Web interface or manually via the steps in this article, and then start thinking about migrating/fixing your FOG server so the partition table layout is optimal and safe so this doesn't happen again.

You really should try to avoid housing your images and snapins on important partitions, and should instead place images and snapins on their own partition. Setting up a partition for images and snapins is most easily done during OS installation - but can be done afterwards albeit there are many more steps and many more chances to make mistakes.

There are numerous tutorials in the Forums and some bits of information about it in the Wiki, but generally you would create a mount point called /images and give that partition as much space as you can. You should still allow the / , possibly /home , and a swap partition the size it needs. For minimal installs, the / partition at minimum can operate on 6GB but I would recommend 20GB. The swap partition should be equal to the amount of RAM, or double. The /home partition should be sizable if you are using a GUI, something like 20GB. If not using a GUI, probably 10GB would be fine. Optionally, you can also create a partition for /opt and give it 20 or so GB.

For Linux newcomers, it's important to note that if your using a GUI to install the OS, setting these partitions is usually intuitive and very easy now-a-days.

Ubuntu 13.04 14.04 15.04 and higher with FOG 1.2.0

Ubuntu has issues with mysql. Particularly anything 13 and greater seems to be hugely a problem from my experience.

When this happens, fog will run normally after the server boots for 10 or 15 minutes and then mysql crashes, which forces a "Update the Database Schema" message when trying to use fog, and the schema updater does not fix the problem.

To test if this is the issue, simply try to restart MySQL (please note this is only temporary) and see if the problem goes away:

sudo service mysql restart

A fix has been reported with this issue. Here are the instructions to fix it:

Open this file:

sudo vi /var/www/fog/lib/fog/Config.class.php

Notate both the host, username & password and then close the above file. Open this file:

sudo vi /opt/fog/.fogsettings

Fill in the following portions:

  • snmysqluser="{root}"
  • snmysqlpass="{PasswordIfYouHaveOne}"
  • snmysqlhost="{localhost}"

Reset the mySQL database password to be what is in the config files.

Then run this:

sudo dpkg-reconfigure mysql-server-5.5

Enter in the new password when prompted.

If you still have issues re-run the installer.

The DB and Multicast

For issues with Multicast, the DB tables associated with that could be dirty. You'll know this is the case if clients just sit at the partclone screen doing nothing.

TRUNCATE TABLE multicastSessions; 
TRUNCATE TABLE multicastSessionsAssoc; 
DELETE FROM tasks WHERE taskTypeId=8;

Via MySQL cli or phpmyadmin (easy to install)

Please also see: Troubleshoot Downloading - Multicast and Multicast

Database Maintenance Commands

Sometimes, a host will be created with an ID of 0 (zero). Sometimes, there are MAC addresses that loose their association with a host, and in a sense become orphaned. Sometimes there are tasks that just need cleared out. Sometimes there are hosts without MACs. Sometimes groups of ID 0 get made, sometimes snapins of ID 0 get made. Sometimes snapins are associated with hosts that don't exist anymore. Other things go wrong sometimes. These things cause problems with FOG's operation and need cleared out in order to have a clean & healthy database. The below commands are intended to run on FOG 1.3, 1.4, and 1.5 series, they will clear these problems for you. This also fixes problems with multicast occasionally, where the partclone screen just sits there doing nothing.

# No password:
mysql -D fog

# Password:
mysql --user=UsernameHere --password=PasswordHere -D fog

# The following chunk of commands will clean out most problems and are safe:
DELETE FROM `hosts` WHERE `hostID` = '0';
DELETE FROM `hostMAC` WHERE hmID = '0' OR `hmHostID` = '0';
DELETE FROM `groupMembers` WHERE `gmID` = '0' OR `gmHostID` = '0' OR `gmGroupID` = '0';
DELETE FROM `snapinGroupAssoc` WHERE `sgaID` = '0' OR `sgaSnapinID` = '0' OR `sgaStorageGroupID` = '0';
DELETE from `snapinAssoc` WHERE `saID` = '0' OR `saHostID` = '0' OR `saSnapinID` = '0';
DELETE FROM `hosts` WHERE `hostID` NOT IN (SELECT `hmHostID` FROM `hostMAC` WHERE `hmPrimary` = '1');
DELETE FROM `hosts` WHERE `hostID` NOT IN (SELECT `hmHostID` FROM `hostMAC`);
DELETE FROM `hostMAC` WHERE `hmhostID` NOT IN (SELECT `hostID` FROM `hosts`);
DELETE FROM `snapinAssoc` WHERE `saHostID` NOT IN (SELECT `hostID` FROM `hosts`);
DELETE FROM `groupMembers` WHERE `gmHostID` NOT IN (SELECT `hostID` FROM `hosts`);
DELETE FROM `tasks` WHERE `taskStateID` IN ("1","2","3");
DELETE FROM `snapinTasks` WHERE `stState` in ("1","2","3");
TRUNCATE TABLE multicastSessions; 
TRUNCATE TABLE multicastSessionsAssoc; 
DELETE FROM tasks WHERE taskTypeId=8;

# This one clears the history table which can get pretty large:

# This one will clear the userTracking table, This table is where user login/logout (for host computers, not the fog server) is stored. This table can also get pretty large.
TRUNCATE TABLE userTracking;