Updated: 28 September 2026 · Applies to: Oracle Database on AlmaLinux 9, Rocky Linux 9, Ubuntu 24.04 and Debian 12
Oracle Database uses Linux semaphores to coordinate its processes. If the kernel allows too few, starting more instances fails with errors such as ORA-27154: post/wait create failed and semget failed with status: 28 ("No space left on device").
Check the current limits
sysctl kernel.sem # four values: SEMMSL SEMMNS SEMOPM SEMMNI
Raise them
Use the values from Oracle's installation guide for your version, for example:
echo "kernel.sem = 250 32000 100 128" > /etc/sysctl.d/97-oracle.conf sysctl --system
Then start the instances again. ipcs -s shows the semaphores in use.
Note: Oracle's preinstall package (oracle-database-preinstall-*) sets these and other kernel parameters automatically on Oracle Linux and RHEL-compatible systems.
