Why is Linux’s buff/cache so large and how to clear it automatically

Running free -h on a Linux host can reveal that the buff/cache line occupies more than 1 GB, which reduces the memory available for other processes.

The buff/cache value represents file data cached by the kernel as a result of normal read/write operations; it is not released automatically when memory becomes scarce.

A direct way to free this memory is to write specific values to /proc/sys/vm/drop_caches:

# Free pagecache only
 echo 1 > /proc/sys/vm/drop_caches
# Free dentries and inodes
 echo 2 > /proc/sys/vm/drop_caches
# Free pagecache, dentries and inodes together
 echo 3 > /proc/sys/vm/drop_caches

Executing the commands clears the cache, but the process must be repeated manually each time the issue reappears.

To automate the cleanup, create a shell script (e.g., cleanBuffCache.sh) and schedule it with cron:

#!/bin/bash

echo "Start cleaning cache"
# Ensure all pending writes are flushed
sync; sync; sync
# Wait a short period
sleep 10
# Drop caches
echo 1 > /proc/sys/vm/drop_caches
echo 2 > /proc/sys/vm/drop_caches
echo 3 > /proc/sys/vm/drop_caches
echo "Cache cleaning finished"

Make the script executable: chmod 777 cleanBuffCache.sh Test it with: ./cleanBuffCache.sh Add a cron job to run the script hourly (or at any desired interval):

crontab -e
* 0 * * * /path/to/cleanBuffCache.sh

Save and exit the editor, then verify the entry with crontab -l. The scheduled task will periodically clear the kernel’s file cache, preventing buff/cache from growing excessively.