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tr '[:upper:]' '[:lower:]' < /var/log/syslog | grep -oE '[[:alnum:]_]+' | sort | uniq -c | sort -nr | head -n 5

grep -iE 'failed|failure|invalid' /var/log/auth.log
grep -iE 'failed|failure|invalid' /var/log/auth.log | wc -l

grep -E ' install | upgrade | remove ' /var/log/dpkg.log | tail -n 50