10 System Information

Learning objectives

Command	Purpose	Meaning	Basic usage	Example
`uname`	View kernel information	Unix name; shows kernel and architecture information	`uname [options]`	`uname -a`
`hostname`	View or set hostname	Shows the current machine name	`hostname`	`hostname`
`uptime`	View uptime and load	Shows uptime, user count, and load average	`uptime`	`uptime`
`date`	View or set time	Shows current date and time	`date`	`date`
`free`	View memory	Shows memory and swap use	`free [options]`	`free -h`
`df`	View disk space	Disk free; shows filesystem free space	`df [options]`	`df -h`
`du`	View directory use	Disk usage; totals file or directory size	`du [options] path`	`du -sh -- .`
`lsblk`	View block devices	List block devices; lists disks and partitions	`lsblk`	`lsblk`
`lscpu`	View CPU information	List CPU; shows CPU architecture and core count	`lscpu`	`lscpu`

Show system and host information:

uname -a
hostname
date
uptime

View memory:

free -h

View disk space:

df -h
df -ih

View item sizes in the current directory:

du -sh -- ./*

View disks and CPU:

lsblk
lscpu

-h commonly means human-readable sizes in KB, MB, and GB.
df -h shows filesystem free space; du -sh shows actual directory use.
df -i shows inodes. Having free capacity does not prove you can create another file.
du -sh -- ./* excludes hidden entries and can be slow in a large directory containing many files; a script must state its scan scope.
Interpret uptime load average with the CPU core count; it is not a simple percentage.
lsblk only displays devices and partitions. Do not casually format or mount disks.
free, ps, and uptime commonly come from procps-ng; lsblk and lscpu from util-linux. Minimal containers and macOS/BSD can lack them.
Linux commonly uses free memory as cache. For troubleshooting, focus on available, swap, and sustained trends rather than the free column alone.
In a container, commands can show different namespace, cgroup, or host views. Do not automatically interpret output as the container limit.

uname -srm
uptime
free -h
df -h -- .
df -ih -- .
du -sh -- .
lscpu | sed -n '1,12p'

A report must distinguish a momentary snapshot, trend, and unknowns. Do not claim a root cause from one load or memory output.