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Follow a log file live and filter by keywords

harmless rootLogsdebian, ubuntu
Adjust the values, the command updates live
root@server
tail -f /var/log/syslog | grep --line-buffered -iE "error|warn|fail"

Follows a log file in real time and lets through only lines matching the pattern (case insensitive). Separate multiple terms with |. --line-buffered makes every matching line appear immediately instead of waiting until the buffer is full.

Note: tail -F instead of tail -f keeps following the file after a log rotation.

Also searched as

  • tail -f show only errors
  • filter log live
  • watch only certain log lines
  • tail and grep log file

Related one-liners

All in Logs

Follow the error log of a Plesk domain live

#tail -f /var/www/vhosts/system/example.com/logs/error_log
harmlessLogs

Analyze Googlebot requests in the access log

#grep -i "googlebot" /var/www/vhosts/system/example.com/logs/access_ssl_log | awk '{print $7}' | sort | uniq -c | sort -rn | head -20
harmlessLogs

Analyze server errors (5xx) in the access log

#awk '$9 ~ /^5[0-9][0-9]$/ {print $9, $7}' /var/www/vhosts/system/example.com/logs/access_ssl_log | sort | uniq -c | sort -rn | head -20
harmlessLogs

Show only error messages in the system journal

#journalctl -p err -b --no-pager
harmlessLogs

Capture network traffic on a port with tcpdump

#tcpdump -i any -nn -c 100 port 25
harmlessNetwork

Check all MySQL tables for errors

#mysqlcheck --all-databases --check --silent
harmlessMySQL and MariaDB

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The commands on myline.de act directly on servers, files and databases. A wrong path or placeholder can delete data irreversibly or make a server unreachable.

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  • Make a backup first and, if possible, try it on a test system.
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