Linux-Commands-pt1
Linux Commands
These are some useful Linux commands that I find myself using over and over. Expect this list to grow over time.
In order to not have an endless page of content, see the related pages
Show top n process for CPU and MEM
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ps -eo comm,pcpu --sort -pcpu | head -5; ps -eo comm,pmem --sort -pmem | head -5
Example
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user01@svr01:~$ ps -eo comm,pcpu --sort -pcpu | head -5; ps -eo comm,pmem --sort -pmem | head -5
COMMAND %CPU
fwupd 0.8
pihole-FTL 0.1
systemd 0.0
kthreadd 0.0
COMMAND %MEM
gnome-shell 1.8
Xorg 0.8
fwupd 0.8
systemd-journal 0.6
That’s a lot to remember, so instead you can just Alias it. Alias (in shells) is just a nice way to “shortcut” commands.
Using the above as an example, lets Alias it into a easier to remember command
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alias top5="ps -eo comm,pcpu --sort -pcpu | head -5; ps -eo comm,pmem --sort -pmem | head -5"
So now, all we need to do is run “top5” and it will execute our chained command
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milo@svr01:~$ top5
COMMAND %CPU
fwupd 0.5
pihole-FTL 0.1
systemd 0.0
kthreadd 0.0
COMMAND %MEM
gnome-shell 1.8
Xorg 0.8
fwupd 0.8
systemd-journal 0.6
Check for listening ports
On Linux
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sudo netstat -tunlp
Will display something like
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root@net-tools:~# sudo netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 310091/systemd-reso
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 310074/sshd: /usr/s
tcp6 0 0 :::22 :::* LISTEN 310074/sshd: /usr/s
udp 0 0 127.0.0.53:53 0.0.0.0:* 310091/systemd-reso
Various Linux commands
cat, less, head, tail, wc, nl
cat Short for concatenate, allows you to combine and display the contents of multiple files. This command on a single file will enable you to display its contents.
less The less command allows you to view the contents of a file one page at a time. Compared to the cat command, this allows you to easily review the contents without being overwhelmed by the large quantity of the log file.
head The head command lets you view the contents at the top of the file. To specify the number of lines to be displayed, use the -n option together with the count of lines, similar to the command below.
tail In contrast to the head command, the tail command allows you to view the end of the file easily. Like the head command, you can specify the number of lines displayed using the -n option (as shown in the command below).
wc The wc command stands for word count. It’s a command-line tool that counts the number of lines, words, and characters in a text file. By default, it prints the count of lines, words, and characters as shown in your terminal, so we can use the -l option to display the line count only.
nl The nl command stands for number lines. It renders the contents of the file in a numbered line format
cut The cut command allows you to extract specific sections (columns) of lines from a file or input stream by “cutting” the line into columns based on a delimiter and selecting which columns to display. This can be done using the -d option (for delimiter) and the -f for position.
sort Command used to sort the lines of text files or input streams in ascending or descending order.
uniq Command allows you to filter out and display unique lines from a sorted file or input stream. Note: The uniq command requires a sorted list to be effective because it only compares the adjacent lines.
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