/usr/libexec/mysqld: Can’t create/write to file ‘/tmp/’ (Errcode: 13)

I‘m using Red Hat Enterprise Linux server version 4.0+ and MySQL version 4.20+. Monit has recently notified me following error:
mysqld’ failed to start.

A detailed log from /var/log/mysqld.log file:

[donotprint]

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	None
Est. reading time	1m

[/donotprint]

/usr/libexec/mysqld: Can’t create/write to file ‘/tmp/ibCfJwf1’ (Errcode: 13)
070420 10:07:58 InnoDB: Error: unable to create temporary file; errno: 13
070420 10:07:58 [ERROR] Can’t init databases
070420 10:07:58 [ERROR] Aborting

070420 10:07:58 [Note] /usr/libexec/mysqld: Shutdown complete

/etc/init.d/mysql start command returned following output:
Initializing MySQL database: [ OK ] Timeout error occurred trying to start MySQL Daemon.
Starting MySQL: [FAILED]

How do I fix this problem on Linux or Unix-like systems?

This error means, MySQL server is not able to access your /tmp directory, to write and create temporary files. Make sure /tmp directory is owned by root user and sticky bit is set on /tmp directory. Type the following commands to fix this error. You must be login as root user and type:

# chown root:root /tmp
# chmod 1777 /tmp
## test it ##
# /etc/init.d/mysqld start

Now, your mysql server should start without a problem.

A note about SELinux and AppArmor security policies

If you are using SELinux or AppArmor with customized data directory for database, you need to modify polices to allow MySQL to read and write to the data directory.

Category	List of Unix and Linux commands
Disk space analyzers	ncdu • pydf
File Management	cat
Firewall	Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04
Network Utilities	NetHogs • dig • host • ip • nmap
OpenVPN	CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04
Package Manager	apk • apt
Processes Management	bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time
Searching	grep • whereis • which
User Information	groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w
WireGuard VPN	Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04