Overview

Notes on Unix commands.

jq

A command to process data in JSON format.

echo '[{"name": "Tom", "age": 20}}]' | jq .

Besides Pretty Print, you can extract data by specifying properties from objects, get the length of objects, and use it in various other ways.

Outputs standard input to both standard output and a file. Can be used with sudo. Overwrites without options, appends with option -a.

echo 'hello world' | sudo tee ./sample.txt

In the case of redirection, > overwrites, >> appends. sudo cannot be used.

Allows you to schedule the execution time of a command.

at -f ./sample.txt 2230

There are various formats for the date and time part.

Creates a file with a random name under the /tmp directory.

mktemp

List of open files Outputs files opened by processes.

-i Filters output by port number.

-i tcp or udp Filters output by TCP or UDP.

-P Outputs port numbers as digits.

-n Outputs without reverse DNS lookup of IP addresses to hostnames.

Examines the port status of a target host over the network.

nmap 192.168.33.10

A command to temporarily suspend file system I/O.

Temporarily suspends file system I/O (freeze process).

fsfreeze -f /data

Releases file system I/O (unfreeze process).

fsfreeze -u /data

Outputs information about mounted file systems.