Let’s break down what this script does in detail. The script is named clearcache.sh, authored by GJS (homelab-alpha), and its purpose is to drop clean caches and reclaimable slab objects like dentries and inodes on a Linux system. This script ensures that the file system’s caches are cleared, which can help in freeing up memory and improving system performance.

Here’s a detailed explanation:

Script Metadata

  • Filename: clearcache.sh
  • Author: GJS (homelab-alpha)
  • Date: May 18, 2024
  • Version: 1.0.1
  • Description: This script drops clean caches, as well as reclaimable slab objects like dentries and inodes.
  • RAW Script: clearcache.sh

The script is designed to clear system caches, which is particularly useful for system administrators who want to ensure that their Linux systems run efficiently by freeing up unused memory.


Logging Configuration

  • Log Directory: $HOME/.bash_script
  • Log File: $log_dir/clearcache_cron.log

Logging Function

log_message(): This function takes a message as an argument and logs it to the specified log file with a timestamp.

log_message() {
  local log_timestamp
  log_timestamp=$(date +"%Y-%m-%d %T")
  echo "[$log_timestamp] $1" >>"$log_file"
}

Initial Logging

The script starts logging by adding a blank line and a start message to the log file.

echo "" >>"$log_file"
log_message "=== beginning of the log ==="
log_message "INFO: Script execution started."

Root User Check

The script checks if it is being run as root or with sudo. If not, it logs an error message and exits.

if [ "$EUID" -ne 0 ]; then
  log_message "ERROR: This script must be run as root or with sudo."
  log_message "=== end of the log ==="
  exit 1
fi

Log Directory Creation

The script checks if the log directory exists. If not, it attempts to create it and logs the result.

if [ ! -d "$log_dir" ]; then
  mkdir -p "$log_dir" || {
    log_message "ERROR: Unable to create log directory: $log_dir"
    log_message "=== end of the log ==="
    exit 1
  }
  log_message "INFO: Log directory created: $log_dir"
fi

Log File Creation

The script checks if the log file exists. If not, it attempts to create it and logs the result.

if [ ! -f "$log_file" ]; then
  touch "$log_file" || {
    log_message "ERROR: Unable to create log file: $log_file"
    log_message "=== end of the log ==="
    exit 1
  }
  log_message "INFO: Log file created: $log_file"
fi

File System Synchronization

The script synchronizes the file system to ensure all buffered modifications are written to disk.

sync

Clearing Caches

The script checks if the file /proc/sys/vm/drop_caches exists. If it does, it writes 1 to this file to clear the caches and logs the result.

if [ -e /proc/sys/vm/drop_caches ]; then
  echo 1 >/proc/sys/vm/drop_caches
  log_message "INFO: File system caches have been cleared."
else
  log_message "ERROR: File /proc/sys/vm/drop_caches does not exist. Cache clearing failed."
  log_message "=== end of the log ==="
  exit 1
fi

Completion Logging

The script logs a success message indicating that it has completed successfully and ends the log.

log_message "INFO: Script execution completed successfully."
log_message "=== end of the log ==="

Conclusion

The clearcache.sh script is a useful tool for Linux system administrators to free up memory by clearing file system caches. It includes comprehensive logging, checks for necessary permissions, and ensures that log directories and files are created if they do not exist. The script is designed to be run as a cron job, allowing automated clearing of caches at specified intervals.

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Last updated 01 Sep 2024, 10:22 CEST . history