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Essential Linux System Commands and Operations

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CPU Information

Checking CPU Architecture

# Determine if the system is 32-bit or 64-bit
getconf LONG_BIT

Verifying 64-bit Support

cat /proc/cpuinfo | grep flags | grep ' lm ' | wc -l

Displaying CPU Details

lscpu

Example Output - 4 cores, 4 threads:

Architecture:          x86_64
CPU(s):                4
Thread(s) per core:    1
Core(s) per socket:    4

Example Output - 6 cores, 12 threads:

Architecture:          x86_64
CPU(s):                12
Thread(s) per core:    2
Core(s) per socket:    6
Model name:            AMD Ryzen 5 5600X 6-Core Processor

Example Output - ARM aarch64 (8 cores):

Architecture:        aarch64
CPU(s):              8
Vendor ID:           HiSilicon
Model name:          Kunpeng-920

Viewing CPU Instruction Sets

cat /proc/cpuinfo | grep flags

Memory Management

/proc/meminfo

The /proc/meminfo file provides detailed memory usage statistics.

cat /proc/meminfo

Key fields include:

  • MemTotal: Total physical memory
  • MemFree: Free memory
  • MemAvailable: Available memory for new processes
  • SwapTotal: Total swap space
  • SwapFree: Free swap space

free Command

free -m
free -h

Output:

              total        used        free      shared  buff/cache   available
Mem:           15Gi       4.2Gi       8.1Gi       512Mi       2.7Gi        10Gi
Swap:          2.0Gi       0.0Gi       2.0Gi

vmstat Command

vmstat -s

smem for Advanced Memory Reporting

sudo apt install smem
smem -t -k

top and htop

top

Press M in top to sort by memory usage.

sudo apt install htop
htop

Process Memory Usage

ps aux --sort=-%mem

Managing Swap Space

Check current swap:

free -m

Create temporary swap file:

# Create 6GB swap file
sudo dd if=/dev/zero of=/swapfile bs=1G count=6

# Format as swap
sudo mkswap /swapfile

# Set permissions
sudo chmod 0600 /swapfile

# Enable swap
sudo swapon /swapfile

Automated swap creation script:

echo "######alloc swap######"
if [ ! -e /swapfile ];then
    sudo fallocate -l 4G /swapfile
    sudo chmod 600 /swapfile
    sudo mkswap /swapfile
    sudo /bin/sh -c 'echo  "/swapfile \t none \t swap \t defaults \t 0 \t 0" >> /etc/fstab'
    sudo swapon -a
fi

Remove swap:

# Disable and remove specific swap
sudo swapoff /swapfile
sudo rm /swapfile

# Disable all swap
sudo swapoff -a

Adjusting /dev/shm Size

Temporary modification:

mount -o size=1500m -o nr_inodes=1000000 -o noatime,nodiratime -o remount /dev/shm

Permanent modification:

tmpfs /dev/shm tmpfs defaults,size=1.5g 0 0
mount -o remount /dev/shm

Disk Operations

Checking Disk Space

lsblk
df -h

Extending Root Partition

View partition layout:

root@host:/# lsblk
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
mmcblk0      179:0    0 57.6G  0 disk
|-mmcblk0p1  179:1    0    4M  0 part
`-mmcblk0p6  179:6    0   14G  0 part /

Delete unused partitions:

root@host:/# fdisk /dev/mmcblk0

Command (m for help): d
Partition number (1-8, default 8): 8

Command (m for help): w

Extend the target partition using parted:

root@host:/# parted /dev/mmcblk0
(parted) resizepart 6
End? [15.4GB]?
(parted) quit

Resize the filesystem:

root@host:/# resize2fs /dev/mmcblk0p6

Fixing Read-Only USB Drives

# Monitor system logs
tail -f /var/log/syslog

# Find the USB device
df -h

# Unmount the USB
umount /media/user/DA18-EBFA

# Repair filesystem
sudo dosfsck -v -a /dev/sda1

Disk Performance Testing

sudo apt-get install hdparm

# Test SSD
sudo hdparm -t /dev/loop0

# Test HDD
sudo hdparm -t /dev/sda1

Mounting and Unmounting Drives

# Create mount point
sudo mkdir /mnt/drive

# Mount Windows drive
sudo mount -t drvfs C:\\ /mnt/c

# Mount SD card
mount /dev/mmcblk1p1 /mnt/sd

# Unmount
sudo umount /mnt/drive

Disk Partitioning

Create new partition:

# View available disks
lsblk

# Start fdisk
sudo fdisk /dev/sda
n           # New partition
p           # Primary partition
3           # Partition number
t           # Change type
8e          # Linux LVM type
w           # Write and exit

# Create filesystem
sudo mkfs -t ext4 /dev/sda3

# Mount partition
sudo mkdir /mnt/sda3
sudo mount /dev/sda3 /mnt/sda3

Delete partition:

sudo fdisk /dev/sda
d           # Delete partition
3           # Partition number
w           # Write and exit

sudo umount /dev/sda3

Process Management

# Find process by port
lsof -i :5001
netstat -tunlp | grep 5001

# View process status
cat /proc/PID/status

# Search processes
ps -aux | grep process_name
ps -ef | grep process_name
pgrep process_name

# Kill process
kill -9 PID
killall -9 process_name

# Batch kill processes
ps -ef | grep script.py | xargs kill -9

File Operations

# Directory size
du -sh
du -h --max-depth=1 ./work

# File size
du -sk filename
ls -lh filename

# Secure copy from remote
scp -r user@remote_ip:/remote/path /local/path

# Secure copy to remote
scp -r /local/path user@remote_ip:/remote/path

# Create nested directories
sudo mkdir -p /a/b/c/d

# Merge directory contents
find data/ -name "*.su" | xargs cat > combined.su

# Remove small files
find ./ -size -1k -exec rm {} \

File Type Detection

file executable

# x86_64 binary
ELF 64-bit LSB shared object, x86-64, version 1 (SYSV)

# ARM binary
ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV)

System Information

OS Details

lsb_release -a
cat /etc/issue
cat /etc/os-release
uname -a

Detailed System Commands

uname -a       # Full system info
uname -i       # Hardware platform
uname -n       # Node name
uname -o       # OS name
uname -p       # Processor architecture
uname -r       # Kernel release
uname -v       # Kernel version

GPU Information

lshw -c video

IP Configuration

ip addr show

Shutdown and Reboot

# Shutdown immediately
sudo shutdown -h now
sudo poweroff
halt

# Schedule shutdown
shutdown -h 10        # 10 minutes
shutdown -c            # Cancel shutdown

# Reboot
sudo reboot
sudo shutdown -r now

# Schedule reboot
shutdown -r 10         # 10 minutes
shutdown -r 20:35      # At specific time

Networking

Network Manager Reset

sudo service network-manager stop
sudo rm /var/lib/NetworkManager/NetworkManager.state
sudo service network-manager start

IP Configuration

Temporary IP:

sudo ifconfig eth0 192.168.1.100 up
sudo route add default gw 192.168.1.1 eth0

Persistent IP:

sudo vim /etc/profile
# Add at end:
ifconfig eth0 192.168.1.100 up
route add default gw 192.168.1.1
source /etc/profile

Route Management

# View routes
route -n

# Add default route
sudo route add default gw 192.168.1.1 eth0

# Add host route
sudo route add -host 192.168.1.50 gw 192.168.1.1 eth0

# Add network route
sudo route add -net 192.168.2.0 netmask 255.255.255.0 eth0

# Delete routes
sudo route del default gw 192.168.1.1

DNS Configuration

sudo vim /etc/systemd/resolved.conf
# Add:
DNS=114.114.114.114

Or edit resolv.conf:

sudo vim /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver 223.5.5.5

sudo /etc/init.d/networking restart

Network Interface Details

# View link speed
cat /sys/class/net/eth0/speed

# Detailed interface info
ethtool eth0

Hostname Management

# View hostname
hostname
hostnamectl

# Modify hostname
sudo vim /etc/hostname
127.0.1.1 new_hostname

DHCP Client

dhclient -v eth0

Port Monitoring

netstat -ltpn

Time Operations

# Get timestamp with nanoseconds
date +%Y-%m-%d' '%H:%M:%S.%N

# Millisecond precision
date +%Y-%m-%d' '%H:%M:%S.%N | cut -b 1-23

# Continuous monitoring
while true; do date +%Y-%m-%d' '%H:%M:%S.%N; sleep 0.1; done

Environment Variables

.bashrc Configuration

# Add to ~/.bashrc
export PACKAGE_ROOT=/path/to/package
export LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:${PACKAGE_ROOT}/lib
export PATH=/opt/toolchain/bin:${PATH}

# Apply changes
source ~/.bashrc

Note: Use : as separator on Linux, ; on Windows.

/etc/profile

sudo vim /etc/profile
# Add at end:
export PATH=$PATH:/custom/path
source /etc/profile

List Variables

export -p

Compression Tools

zip/unzip

# Compress directory
zip -vr archive.zip /etc/

# Extract to current directory
unzip archive.zip

# Extract to specific directory
unzip archive.zip -d ./target/

tar

# Create tar.gz
tar -cvzf output.tar.gz /source/directory

# Extract tar.gz
tar -xvzf archive.tar.gz
tar -xvzf archive.tar.gz -C /target/directory

# Extract .tar.xz
tar -xJvf archive.tar.xz

7z

sudo apt-get install p7zip-full

# Extract zip
7z x archive.zip -o/target/path

# Extract rar
7z x archive.rar

File Downloads

curl

# Download single file
curl -O https://example.com/file.zip

# Download with progress
curl -# -O https://example.com/file.zip

# Limit speed
curl --limit-rate 1m -O https://example.com/file.zip

# Timeout settings
curl --connect-timeout 30 --max-time 300 https://example.com/file.zip

wget

# Basic download
wget https://example.com/file.tar.gz

# Save with custom name
wget -O output.tar.gz https://example.com/file.tar.gz

# Download to directory
wget -P /usr/software https://example.com/file.tar.gz

# Resume download
wget -c https://example.com/large-file.tar.gz

# Background download
wget -b https://example.com/file.tar.gz

# Skip SSL verification
wget --no-check-certificate https://example.com/file.tar.gz

Symbolic Links

# Create symlink
ln -s /source/path /link/path

# Remove symlink
rm -rf /link/path

# Modify symlink
ln -snf /new/target /link/path

File Integrity Verification

MD5 Checksum

# Generate checksum
md5sum -b file.bin > file.bin.md5

# Verify file
md5sum -c file.bin.md5

SHA256 Checksum

# Generate checksum
sha256sum -b archive.tar.gz > archive.tar.gz.sha256

# Verify file
sha256sum -c archive.tar.gz.sha256

Binary Analysis Tools

ldd - Library Dependencies

ldd /path/to/binary

file - Binary Type Detection

file /path/to/binary

nm - Symbol Table

nm binary | grep GLIBC_

strings - Embedded Strings

strings binary | grep GLIBCXX

readelf - ELF Analysis

# File header
readelf -h binary

# Dynamic section
readelf -d binary

Network Configuration

ifconfig

# List all interfaces
ifconfig -a

# Enable interface
sudo ifconfig eth0 up

# Set IP address
sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0

ldconfig - Library Cache

# Update library cache
sudo ldconfig

# Search for library
ldconfig -p | grep library_name

Add library path:

sudo vim /etc/ld.so.conf.d/custom.conf
# Add library path
sudo ldconfig

pkg-config

# Get package version
pkg-config --modversion package_name

# Get include paths
pkg-config --cflags package_name

# Get library paths
pkg-config --libs package_name

# List all packages
pkg-config --list-all

# Search packages
pkg-config --list-all | grep search_term

Quick Space Allocation

# Preallocate 2GB file
fallocate -l 2G testfile.dat

# Difference from dd:
# fallocate: instant allocation, no data written
# dd: writes actual data, slower

Kernel Messages

dmesg | grep driver_name
Tags: Linuxsystem-administrationcommand-line
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