SysAdmin

This page has useful snippets for sysadmin tasks, shell scripting, and other related things used frequently(and unfrequently) for things like managing servers, firewalls, networking, monitoring and so on.

CPU Usage w/ no external tools

This snippet(s) gets the CPU usage of the system using /proc/stat over the course of 0.5 seconds. this can be changed to 1 second for a more accurate reading.

CPU Usage

prev_idle=$(awk '/^cpu /{print $5}' /proc/stat)
prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)

sleep 0.5

idle=$(awk '/^cpu /{print $5}' /proc/stat)
total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)

diff_idle=$((idle - prev_idle))
diff_total=$((total - prev_total))

usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l)
echo "$usage"

Same command but in a single line:

CPU Usage One-liner

prev_idle=$(awk '/^cpu /{print $5}' /proc/stat); prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); sleep 0.5; idle=$(awk '/^cpu /{print $5}' /proc/stat); total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); diff_idle=$((idle - prev_idle)); diff_total=$((total - prev_total)); usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l); echo "$usage"

Every Second

CPU Usage Every Second

while true
do
    prev_idle=$(awk '/^cpu /{print $5}' /proc/stat)
    prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)

    sleep 0.5

    idle=$(awk '/^cpu /{print $5}' /proc/stat)
    total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)

    diff_idle=$((idle - prev_idle))
    diff_total=$((total - prev_total))

    usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l)
    echo "$usage%"
done

One liner for the above:

CPU Usage Every Second One-liner

while true; do prev_idle=$(awk '/^cpu /{print $5}' /proc/stat); prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); sleep 0.5; idle=$(awk '/^cpu /{print $5}' /proc/stat); total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); diff_idle=$((idle - prev_idle)); diff_total=$((total - prev_total)); usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l); echo "$usage%"; done

Alternative command to above

Does the same thing but differently

CPU Usage Alternative

_STAT_PREV_IDLE=$(awk '/^cpu /{print $5}' /proc/stat)
prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)
while true
do
    sleep 0.5
    idle=$(awk '/^cpu /{print $5}' /proc/stat)
    total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat)
    diff_idle=$((idle - prev_idle))
    diff_total=$((total - prev_total))
    usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l)
    echo "CPU Usage: $usage%"
    prev_idle=$idle
    prev_total=$total
done

One liner for the above:

CPU Usage Alternative One-liner

_STAT_PREV_IDLE=$(awk '/^cpu /{print $5}' /proc/stat); prev_total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); while true; do sleep 0.5; idle=$(awk '/^cpu /{print $5}' /proc/stat); total=$(awk '/^cpu /{s=0; for(i=2;i<=NF;i++) s+=$i; print s}' /proc/stat); diff_idle=$((idle - _STAT_PREV_IDLE)); diff_total=$((total - prev_total)); usage=$(echo "scale=1; 100 * ($diff_total - $diff_idle) / $diff_total" | bc -l); echo "CPU Usage: $usage%"; _STAT_PREV_IDLE=$idle; prev_total=$total; done

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Memory Usage w/ no external tools

Memory Usage

while true
do
    awk '/^MemTotal:/{total=$2}/^MemAvailable:/{avail=$2} END{used=total-avail; usage=(used/total)*100; used_gb=used/1024/1024; printf("RAM Usage: %.2f%%  %.2fGB\n", usage, used_gb)}' /proc/meminfo
    sleep 0.5
done

One-liner for the above:

Memory Usage One-liner

while true; do awk '/^MemTotal:/{total=$2}/^MemAvailable:/{avail=$2} END{used=total-avail; usage=(used/total)*100; used_gb=used/1024/1024; printf("RAM Usage: %.2f%%  %.2fGB\n", usage, used_gb)}' /proc/meminfo; sleep 0.5; done