Useful Shell Command Reference

There are many ways to get information about hardware:

$ cat /proc/cpuinfo
$ lscpu

$ cat /proc/meminfo
$ vmstat -s
$ free -m or free -g

$ ip link show
$ netstat -i

$ lsblk -d
$ fdisk -l

$ virt-what

df or mount show the disks mounted and can be used to show disk space.

On a file or directory level, the du command is useful for seeing how much disk space is being used.

iostat and sar come with Linux package sysstat-9.0.4-27. iostat is used for tracking I/O performance. The recommended options are:

• -d for disk utilization
• -m for calculations in MB/sec
• -x for extended report
• -t sec to repeat statistics every sec seconds

sar has several forms of output:

• -b for I/O and transfer rate statistics
• -d for block device activity
• -n for network statistics
• -v for various file system statistics

lsof is used to identify mapping between processes and open files. By passing multiple arguments, lsof can be used to help isolate the output:

• lsof <filename> to list processes that have <filename> open.
• lsof -p <pid> to list all files opened by the process corresponding to <pid>.
• lsof -r <secs> to keep producing output with a period of <secs>.

• nc (netcat) or ss (socket statistics) are good for showing network activity.
• netstat is the Swiss-army knife tool for network interfaces.
• tcpdump or Wireshark with Kafka filter should be good for packet sniffing.

• top shows a sorted list of processes.
• ps shows a snapshot list of processes. Arguments can be used to filter the output.
• ps -o min_flt,maj_flt pid shows page fault information.

• ulimit -a is used to display kernel limits and shows which flags affect which kernel settings.
• ulimit -n FD to set a limit on open file descriptors.