Some useful commands for Linux administration
I will update this page as I come across more interesting and less-known commands for Linux Administration, for my and your reference.
Resource Management
View the CPU load of a specific process only
top -p $(pgrep -d, appserver)
Limit the CPU usage of a process to 25%
cpulimit -e backup.sh -l 25
Migrate a running process to a different CPU core without restarting it
taskset -p 2 <PID>
Bind a process to specific CPU cores
taskset -c 0,2 <app>
Check which NUMA (Non-Uniform Memory Access) nodes a process is using
cat /proc/<PID>/numa_maps
Show processes actively using I/O and their real-time disk I/O usage
iotop -o
Storage Management
Unlock and mount a LUKS-encrypted partition
cryptsetup luksOpen /dev/sdb1 secure_data && mount /dev/mapper/secure_data /mnt/secure
Unmount and close/re-lock a LUKS-encrypted partition
umount /mnt/secure && cryptsetup luksClose secure_data
Create a RAID 5 array using 3x specified disks
mdadm --create --level=5 --raid-devices=3 /dev/md0 /dev/sdb /dev/sdc /dev/sdd
Increase LV /mountpoint to have exactly 25G available, as a one-liner
lv=$(df /mountpoint --output=source | tail -1); free=$(df --output=avail -BG /mountpoint | tail -1 | tr -dc 0-9); [ $free -lt 25 ] && lvresize -r -L +$((25 - free))G "$lv"
Networking
Set up a static route so that all traffic to a specific IP goes through a specific network interface
ip route add 192.168.2.0/24 dev eth1
Execute a self-test on a NIC
ethtool -t eth0
Using a list of hostnames in a file, test whether each one can reach the internet
for i in $(cat hostnames.txt); do output=$(ssh -q $i "timeout 3 bash -c 'echo >/dev/tcp/1.1.1.1/443' && echo online || echo offline") echo "$i - $output"; done
Text Manipulation
Make the first ‘column’ of a file lowercase, leave the rest as-is
awk -F'\t' 'BEGIN{OFS=FS} {$1=tolower($1); print}' input.txt
AWS CLI
List all AWS EC2 instances in the current account, including instance ID, name and private and public IP addresses
aws ec2 describe-instances --query "Reservations[*].Instances[*].[InstanceId, Tags[?Key=='Name']|[0].Value, PrivateIpAddress, PublicIpAddress]" --output text