Master Linux System Monitoring: Directories, CPU, Memory, Disk & Essential Commands

Directory Structure

Directory

Description

/bin

Executable files

/boot

Kernel and boot files

/dev

Device files

/etc

Configuration information

/etc/rc.d

Scripts used during shutdown/startup

/etc/rc.d/init.d

Default service start scripts

/etc/xinetd.d

Service startup definitions

/etc/X11

X Window configuration files

/lib

Libraries needed for program execution or compilation

/proc

Kernel and process information stored in memory

/root

Root user's home directory

/sbin

System administration binaries

/tmp

Temporary files

/usr

Programs and utilities (similar to Windows "Program Files")

Key directories to master are /etc and /proc .

Monitoring

View CPU Details

CPU information resides in /proc/cpuinfo. Use: cat /proc/cpuinfo Sample output (truncated):

processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 60
model name  : Intel(R) Pentium(R) CPU G3260 @ 3.30GHz
stepping    : 3
cpu MHz     : 800.000
cache size  : 3072 KB
physical id : 0
siblings    : 2
core id     : 0
cpu cores   : 2
...

Important fields are processor , physical id , siblings , core id and cpu cores . The diagram below explains their meaning:

The server has one physical CPU with two logical processors (threads) and two cores.

Query Logical CPU Count

cat /proc/cpuinfo | grep "processor" | wc -l

Query Physical CPU Count

cat /proc/cpuinfo | grep "physical id" | sort | uniq | wc -l

Query Core Count per Physical CPU

cat /proc/cpuinfo | grep "core id" | wc -l

CPU Utilization

Use top to view real‑time CPU usage, process IDs, memory usage, etc.

Linux Version Information

Two ways:

cat /proc/version

lsb_release -a

Sample output:

Linux version 2.6.32-431.el6.x86_64 ([email protected]) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC) ) #1 SMP Sun Nov 10 22:19:54 EST 2013
LSB Version:    :base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID: RedHatEnterpriseServer
Description:    Red Hat Enterprise Linux Server release 6.5 (Santiago)
Release:        6.5
Codename:       Santiago

Memory Information

Commands:

cat /proc/meminfo
free -m
top

Sample free -m output:

total       used       free     shared    buffers     cached
Mem:          7747       5392       2355          0        230       3258
-/+ buffers/cache:       1903       5843
Swap:         7999          0       7999

Metric

Meaning

Size

total

Total memory

7747M

used

Memory in use

5392M

free

Free memory

2355M

shared

Always 0 (unused)

0

buffers

Buffer cache

230M

cached

Page cache

3258M

Real memory usage = used - buffers - cached (1903 M). Free memory = free + buffers + cached (5843 M). Heavy swap usage indicates insufficient physical RAM.

Disk Status

Common commands:

df -h      # display sizes in G
fdisk -l   # detailed disk info
lsblk      # tree view of block devices

Sample lsblk output:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0   461G  0 disk 
├─sda1   8:1    0 402.9G  0 part /
├─sda2   8:2    0  50.4G  0 part /home
└─sda3   8:3    0   7.8G  0 part [SWAP]
sr0     11:0    1  1024M  0 rom

Sample df -h output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       397G   21G  356G   6% /
tmpfs           3.8G     0  3.8G   0% /dev/shm
/dev/sda2        50G  180M   47G   1% /home

Charset Related

echo $LANG            # show current locale
locale -a             # list all locales
export LANG=zh_CN.UTF-8   # temporary change
vi /etc/sysconfig/i18n   # permanent configuration

Services

Firewall Control

# service iptables status
# service iptables start
# service iptables stop
# service iptables restart

FTP Service Control

# service vsftpd status
# service vsftpd start
# service vsftpd stop
# service vsftpd restart

Common Commands

View Text Files

cat file.txt
tail -n 5 /proc/cpuinfo
vim file.txt

sed (Stream Editor)

Reference: https://man.linuxde.net/sed

Modify System Time

date -s "20160408 12:52:00"   # set system time
hwclock --systohc               # sync hardware clock to system clock
hwclock --hctosys               # sync system clock to hardware clock

File Search (find)

find /home -name "*.txt"

Remote Copy (scp)

# copy from remote to local
scp -r [email protected]:/opt/soft/mongodb /opt/soft/
# copy from local to remote
scp /opt/soft/mysql-5.6.0.tar.gz [email protected]:/opt/soft/scptest
# copy between remotes
scp -r [email protected]:/opt/soft/mongodb [email protected]:/opt/soft

Directory Operations

mkdir -p /tmp/aa/bb/cc
rmdir /tmp/aa   # only removes empty directories

File Deletion (rm)

rm -rf /tmp/aa

File Move/Rename (mv)

mv /tmp/test.file /tmp/lib/
mv /tmp/test.file /tmp/lib/test1.file

Check Logged‑in Users

who
whoami

System Reboot

reboot

Ping Test

ping 159.179.160.43 -t

Change Permissions (chmod)

chmod u+rwx,g+rw,o+r aa.txt
chmod 764 aa.txt

Change Owner/Group (chown)

chown weblogic nohup.log          # change owner
chown :weblogic nohup.log         # change group
chown weblogic:weblogic nohup.log # change both

Compression & Extraction

# Create tar archive
tar cvf backup.tar /etc
# Compress
gzip backup.tar   # -> backup.tar.gz
bzip2 backup.tar  # -> backup.tar.bz2
# Equivalent one‑liner
tar cvfz backup.tar.gz /etc
# Extract
gunzip backup.tar.gz
tar xvf backup.tar

Process Management (ps, kill)

ps -ef | grep java
kill 11588            # graceful
kill -9 11588         # force
pkill -9 java

Network Connections (netstat)

Common options: -a all, -t TCP, -u UDP, -n numeric, -l listening, -p show program, -r routing table.

netstat -antup | grep ssh
netstat -r

Linux Configuration Files

File

Purpose

/etc/profile

Global environment variables

~/.bash_profile

User‑specific environment variables

/etc/xinetd.conf and /etc/xinetd.d/*

Service configuration

/etc/rc.d/rc.local

Startup script