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Get the first real error message with time information in the journal, service and kernel log instead of the general warning on the screen.
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The OOM Killer is the kernel mechanism that keeps the system alive by terminating processes when the system or a cgroup cannot provide the required memory. A high used value alone is not a problem; MemAvailable, swap, process RSS, cgroup limits and kernel OOM records must be read together.
kernel: Out of memory: Killed process 2451 (php-fpm) total-vm:...
systemd-oomd: Killed /user.slice/...
Cannot allocate memoryThe OOM Killer is the kernel mechanism that keeps the system alive by terminating processes when the system or a cgroup cannot provide the required memory. A high used value alone is not a problem; MemAvailable, swap, process RSS, cgroup limits and kernel OOM records must be read together.
Get the first real error message with time information in the journal, service and kernel log instead of the general warning on the screen.
Test service, disk, network, permission, security policy and application configuration separately without changing them at the same time.
The service name, package manager and firewall tool may be different on Ubuntu/Debian and AlmaLinux/Rocky/CloudLinux.
Keep a second session, console, snapshot or current backup for SSH, network, firewall, boot and disk changes.
Do not use the 'echo 3 > drop_caches' command as a permanent fix.
Meaning: The kernel terminated a process to free memory.
Possible cause: RAM/swap is exhausted or an uncontrolled process grew.
Meaning: The userspace OOM manager terminated the unit/cgroup due to pressure.
Possible cause: Memory pressure or swap policy.
Meaning: The process could not allocate new memory.
Possible cause: System/cgroup limit, overcommit or address space.
Meaning: Swap tamamen dolu.
Possible cause: Continuous memory pressure or low RAM.
Meaning: The web worker was terminated due to memory.
Possible cause: Heavy request, memory leak, or excessive child.
Meaning: The database process was selected as the victim.
Possible cause: The total buffer and other services exceeded RAM.
Meaning: The container memory limit was exceeded.
Possible cause: Low limit or application leak.
Meaning: Linux is using cache but there is no pressure.
Possible cause: Normal page cache usage.
No error records were found matching this expression.
free -h
cat /proc/meminfo | grep -E 'MemTotal|MemAvailable|SwapTotal|SwapFree|CommitLimit|Committed_AS'Shows RAM, available, swap and commit values.
ps -eo pid,user,comm,rss,vsz,%mem,%cpu --sort=-rss | head -n 30Shows the large processes by RSS.
journalctl -k -g 'Out of memory|Killed process|oom-kill' -n 200 --no-pagerShows the kernel OOM events.
cat /proc/pressure/memory
vmstat 1 10Shows memory pressure, paging and swap activity.
swapon --show --bytes
cat /proc/sys/vm/swappinessShows the swap areas and the swappiness value.
systemctl show servisadi -p MemoryCurrent -p MemoryPeak -p MemoryMax -p MemoryHigh -p OOMPolicyShows the service cgroup memory usage and limits.
systemd-oomd, snap/container processes and unattended operations must also be monitored.
systemctl status systemd-oomd --no-pager 2>/dev/null || trueoomctl 2>/dev/null || truesystemd-cgtop -b -n 1cgroup v2, tuned profile, LVE limits and kernel OOM records must be examined together.
systemd-cgtop -b -n 1tuned-adm active 2>/dev/null || truelveinfo --period=1h --by-fault=mem 2>/dev/null | head -n 40 || truePHP-FPM pool, MySQL/MariaDB buffer, mail filters and backup processes must be evaluated against the total RAM.
ps -C php-fpm,lsphp,mysqld,mariadbd -o pid,cmd,rss,%mem --sort=-rss 2>/dev/null | head -n 40systemctl list-units --type=service --state=running | grep -E 'php|mysql|maria|backup'free -hRecord the exact on-screen or logged error message with its timestamp, then test the service, network, disk, and security layers separately.
The package manager, firewall, network manager, and some service names differ by distribution family. The distribution section on the page explains these differences.
A restart may restore service temporarily, but restarting before collecting logs and resource data can hide the root cause.
Read-only diagnostic commands are generally safe. Configuration, firewall, disk, and recovery changes require console access, a backup, and a rollback plan.
The Linux layer is the same, but control-panel service wrappers, firewall plugins, and vendor packages must also be considered.
Keep a second session and the provider console open during SSH, firewall, network, or boot changes.
No. Technical accuracy and coverage provide a strong foundation, but rankings also depend on competition, site authority, internal links, speed, and user behavior.
We analyze Ubuntu, Debian, AlmaLinux, Rocky and CloudLinux service, disk, network, security, performance and boot problems with log data.