/run/

/run/ is a "tmpfs" file system for system packages to place runtime data in. This directory is flushed on boot, and generally writable for privileged programs only. Always writable.

/run/
/run/systemd/
/run/lock
/run/pacct_source
/run/nginx.pid
/run/php/php7.2-fpm.sock
/run/rpcbind.sock   

Jan 26 16:23:34 SERVER systemd-logind[876]: Failed to save user data /run/systemd/users/0: No space left on device

apt upgrade
Failed to reload daemon: Refusing to reload, not enough space available on /run/systemd. Currently, 1.9M are free, but a safety buffer of 16.0M is enforced.

Increase /run filesystem space

1) Append to /etc/fstab
 echo "none /run tmpfs defaults,size=256M 0 0" >> /etc/fstab
2) mount /run
3) mount -o remount /run
4) Check /run space: df -h /run

reboot
System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to talk to init daemon.

Activities

• Read "Introducing /run" by Lennart Poettering in 2011 https://lwn.net/Articles/436012/

Related terms

 Apr 13 07:42:02 SERVER systemd[1]: nginx.service: Failed to parse PID from file /run/nginx.pid: Invalid argument

• /dev/shm
• /var/run/

See also

• /run/, /var/run/, /run/systemd/
• 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/
• Systemd: systemctl, systemd-journald, journalctl systemd-cat, systemd-logind, systemd-networkd:networkctl, systemd-timesyncd, systemd-resolved, systemd-udevd , Systemd-logind: loginctl, hostnamectl, udevadm, systemd-run, portablectl, systemd-nspawn, systemd resource management, Timer (systemd), systemd logs, /etc/systemd/, systemd services, systemd-mount, /run/systemd/, .service, /usr/lib/systemd/, /usr/lib/systemd/system/, /usr/lib/systemd/system/systemd-resolved.service, /lib/systemd/, machinectl, systemd-oomd, systemd-analyze

https://wiki.ubuntu.com/DebuggingSystemd