/var/log/

• /var/log/journal/
• /var/log/kern.log
• /var/log/auth.log (sshd logs)
• /var/log/dmesg (not in Ubuntu)
• /var/log/syslog
• /var/log/mysql/error.log (MariaDB)]]
• /var/log/postgresql
• /var/log/mail.log
• /var/log/libvirt/qemu/
• /var/log/nginx/
• /var/log/dpkg.log*
• /var/log/openvpn.log
• /var/log/sysstat/

Related

• No space left on device
• journalctl

See also

• FHS, /proc/, /proc/net/, /boot/, /run/, /dev/, /usr/, /var/run/, /etc/, /var/, /var/lib/ /var/log/, /var/www/, /opt/, /lib/, /sys/, /proc/kcore, /proc/sys/, /proc/sys/vm/, /snap/, /mnt/, /mnt/data, /var/opt/, /usr/bin/, /lib/, /proc/$PID/, /proc/self/
• Linux Logging: logger systemd-cat journalctl, syslog, rsyslogd logrotate, sshd logs, Logwatch, logcheck, Container logging, Journalctl logs, journald.conf, Docker logs, ts