Monitoring

2026-05-23 #system #monitoring #hardware

vmstat, iostat, sar, hardware info, sensors, inotifywait, /proc and /sys. See also journalctl for log analysis and processes for top/htop/btop.

vmstat

Snapshot: vmstat
Every 2 sec, 10 samples: vmstat 2 10
Active/inactive memory: vmstat -a
With timestamps: vmstat -t 1
Disk stats: vmstat -d
In MB: vmstat -S M

Section	Field	Meaning
procs	`r`	runnable (CPU-bound)
procs	`b`	blocked (I/O)
memory	`swpd`	swap used
memory	`free`	free RAM
memory	`buff/cache`	buffers/cache
swap	`si/so`	swap in/out — non-zero so → memory pressure
io	`bi/bo`	blocks in/out per sec
system	`in/cs`	interrupts / context switches
cpu	`us/sy/id`	user/system/idle
cpu	`wa`	I/O wait (high → disk bottleneck)
cpu	`st`	stolen (VM)

iostat

Install sysstat.

Basic: iostat
Extended every 2 sec: iostat -x -t 2
Specific device: iostat -x /dev/nvme0n1
MB/s: iostat -m
CPU only / device only: iostat -c / iostat -d

Extended fields (-x)

Field	Meaning
`r/s`, `w/s`	reads/writes per sec
`rMB/s`, `wMB/s`	throughput
`await`	wait (queue+service) ms
`%util`	device utilization

sar

Install sysstat and enable the collector: sudo systemctl enable --now sysstat

CPU live: sar -u 1 5
Memory: sar -r 1 5
Disk: sar -d 1 5
Network per-iface: sar -n DEV 1 5
Sockets: sar -n SOCK 1 5
Historical CPU from file: sar -u -f /var/log/sa/sa13
Memory in window: sar -r -s 08:00:00 -e 17:00:00

Hardware

CPU summary: lscpu
Per-core info: cat /proc/cpuinfo
Core count: nproc
Memory summary: free -h
Detailed memory: cat /proc/meminfo
PCI devices: lspci / lspci -v / lspci -k
Find GPU: lspci | grep -i vga
USB: lsusb / lsusb -v / lsusb -t
BIOS/DMI: sudo dmidecode sudo dmidecode -t memory sudo dmidecode -t bios sudo dmidecode -t system
Block devices + fs info: lsblk -f
Disk model/firmware: sudo hdparm -I /dev/sda

Sensors:

sudo sensors-detect    # one-time
sensors

Battery: upower -i /org/freedesktop/UPower/devices/battery_BAT0 cat /sys/class/power_supply/BAT0/capacity

Kernel / OS:

uname -a
uname -r
hostnamectl
cat /etc/os-release
uptime

inotifywait

Install inotify-tools.

Watch file (blocks): inotifywait -m /path/to/file
Recursive directory: inotifywait -mr /path/to/dir
Specific events: inotifywait -m -e modify,create,delete /path/to/dir
Formatted with timestamps: inotifywait -mr --format '%T %w%f %e' --timefmt '%F %T' /path/to/dir

Auto-rebuild on change:

inotifywait -mr -e modify --include '\.py$' ./src | while read -r path event file; do
    echo "Change: $file"
    make build
done

One-shot: inotifywait -e modify /etc/hosts && echo "changed"

Event	When
`access`	file read
`modify`	content change
`attrib`	metadata change
`close_write`	RW file closed
`open`	file opened
`moved_to/from`	moved in/out of dir
`create`	created
`delete`	deleted

All-in-one monitors

btop (recommended): btop
glances (with web mode): glances
dstat (one-line stats): dstat -cdngy (cpu, disk, net, page, sys)

ncdu (interactive disk usage)

ncdu /home

watch

Repeat with highlight: watch -d free -h
Socket stats every sec: watch -n 1 "ss -s"

/proc & /sys

System-wide:

cat /proc/cpuinfo
cat /proc/loadavg
cat /proc/meminfo
cat /proc/swaps
cat /proc/uptime
cat /proc/version
cat /proc/filesystems
cat /proc/net/tcp
cat /proc/net/dev

Per-process (replace 1234 with PID):

cat /proc/1234/status
cat /proc/1234/cmdline
cat /proc/1234/environ
ls -la /proc/1234/fd
cat /proc/1234/maps
cat /proc/1234/limits

Kernel tuning via /sys:

cat /sys/block/sda/queue/scheduler
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor