Memory Information

Is the server out of memory? Is something leaking? Let's learn to check.

free - Memory Overview

Terminal

$free -h

total used free shared buff/cache available Mem: 7.7Gi 2.1Gi 3.2Gi 256Mi 2.4Gi 5.1Gi Swap: 2.0Gi 0B 2.0Gi

-h for human-readable sizes.

Understanding the Output

Column	Meaning
total	Total physical RAM
used	RAM in use by applications
free	Completely unused RAM
shared	Shared memory
buff/cache	Memory used for caching
available	Memory available for new apps

free vs available - The Most Confusing Part

Low free doesn't mean trouble. Linux uses "free" RAM for caching to speed things up.

The available column is what matters - it's free + cache that can be reclaimed.

Think of it this way:

free = money in your wallet
buff/cache = money in a jar you can easily break open
available = total money you can spend right now

The Cache Misconception

Terminal

$free -h

total used free shared buff/cache available Mem: 8Gi 2Gi 1Gi 256Mi 5Gi 5Gi

"Only 1GB free!" - Don't panic. 5GB is available because the cache can be reclaimed.

Linux caches disk reads in unused RAM. When an app needs memory, the cache shrinks. This is efficient, not a problem.

Swap

Swap is disk space used when RAM is full:

Terminal

$free -h | grep Swap

Swap: 2.0Gi 500Mi 1.5Gi

Swap usage = 0: Normal, RAM isn't exhausted
Swap usage > 0: RAM pressure, might be slow
Swap full: Bad - system will be very slow or crash

Swap Usage

High swap usage means your system ran out of RAM. Performance degrades significantly. Either add RAM or reduce memory usage.

/proc/meminfo

For detailed stats:

Terminal

$cat /proc/meminfo | head -10

MemTotal: 8045612 kB MemFree: 3382948 kB MemAvailable: 5367132 kB Buffers: 234567 kB Cached: 2345678 kB SwapCached: 0 kB Active: 2456789 kB Inactive: 1234567 kB

Per-Process Memory

Terminal

$ps aux --sort=-%mem | head -10

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND mysql 1234 2.0 15.2 234567 123456 ? Sl Jan14 10:30 mysqld nginx 1235 0.5 5.1 65432 41234 ? S Jan14 1:20 nginx

Or use top/htop and press M to sort by memory.

RSS vs VSZ

Metric	Meaning
RSS	Resident Set Size - actual RAM used
VSZ	Virtual Size - total address space

RSS is the "real" memory usage.

Quick Check Script

hljs bash

echo "=== Memory Usage ==="
free -h
echo ""
echo "=== Top Memory Users ==="
ps aux --sort=-%mem | head -5

Knowledge Check

What does it mean if 'free' memory is low but 'available' memory is high?

Quick Reference

Command	Shows
`free -h`	Memory overview
`free -m`	Memory in MB
`cat /proc/meminfo`	Detailed stats
`ps aux --sort=-%mem`	Processes by memory
`top` then `M`	Real-time, sorted by memory

Key Takeaways

free -h gives memory overview
Check available, not just free
buff/cache is reclaimable - not wasted
Swap usage > 0 indicates RAM pressure
RSS shows actual memory used per process

Next: checking CPU information.

Memory Information

Is the server out of memory? Is something leaking? Let's learn to check.

free - Memory Overview

Terminal

$free -h

total used free shared buff/cache available Mem: 7.7Gi 2.1Gi 3.2Gi 256Mi 2.4Gi 5.1Gi Swap: 2.0Gi 0B 2.0Gi

-h for human-readable sizes.

Understanding the Output

Column	Meaning
total	Total physical RAM
used	RAM in use by applications
free	Completely unused RAM
shared	Shared memory
buff/cache	Memory used for caching
available	Memory available for new apps

free vs available - The Most Confusing Part

Low free doesn't mean trouble. Linux uses "free" RAM for caching to speed things up.

The available column is what matters - it's free + cache that can be reclaimed.

Think of it this way:

free = money in your wallet
buff/cache = money in a jar you can easily break open
available = total money you can spend right now

The Cache Misconception

Terminal

$free -h

total used free shared buff/cache available Mem: 8Gi 2Gi 1Gi 256Mi 5Gi 5Gi

"Only 1GB free!" - Don't panic. 5GB is available because the cache can be reclaimed.

Linux caches disk reads in unused RAM. When an app needs memory, the cache shrinks. This is efficient, not a problem.

Swap

Swap is disk space used when RAM is full:

Terminal

$free -h | grep Swap

Swap: 2.0Gi 500Mi 1.5Gi

Swap usage = 0: Normal, RAM isn't exhausted
Swap usage > 0: RAM pressure, might be slow
Swap full: Bad - system will be very slow or crash

Swap Usage

High swap usage means your system ran out of RAM. Performance degrades significantly. Either add RAM or reduce memory usage.

/proc/meminfo

For detailed stats:

Terminal

$cat /proc/meminfo | head -10

MemTotal: 8045612 kB MemFree: 3382948 kB MemAvailable: 5367132 kB Buffers: 234567 kB Cached: 2345678 kB SwapCached: 0 kB Active: 2456789 kB Inactive: 1234567 kB

Per-Process Memory

Terminal

$ps aux --sort=-%mem | head -10

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND mysql 1234 2.0 15.2 234567 123456 ? Sl Jan14 10:30 mysqld nginx 1235 0.5 5.1 65432 41234 ? S Jan14 1:20 nginx

Or use top/htop and press M to sort by memory.

RSS vs VSZ

Metric	Meaning
RSS	Resident Set Size - actual RAM used
VSZ	Virtual Size - total address space

RSS is the "real" memory usage.

Quick Check Script

hljs bash

echo "=== Memory Usage ==="
free -h
echo ""
echo "=== Top Memory Users ==="
ps aux --sort=-%mem | head -5

Knowledge Check

What does it mean if 'free' memory is low but 'available' memory is high?

Quick Reference

Command	Shows
`free -h`	Memory overview
`free -m`	Memory in MB
`cat /proc/meminfo`	Detailed stats
`ps aux --sort=-%mem`	Processes by memory
`top` then `M`	Real-time, sorted by memory

Key Takeaways

free -h gives memory overview
Check available, not just free
buff/cache is reclaimable - not wasted
Swap usage > 0 indicates RAM pressure
RSS shows actual memory used per process

Next: checking CPU information.