Basic Commands

Commands

• ls , pwd , cd

• mkdir, rmdir, rm -r → remove non-empty dirs

• touch , cat > file.ext → overrides, cat >> file.ext → appends, cat file.ext → prints

• find <dir/path> -name “expression” → expression is CASE SENSITIVE

  

  • use iname for IGNORE CASE SENSITIVE..

    

• find <dir/path> -type <f/d> -name “exp” → f for files, d for dirs

• more find commands - https://www.tecmint.com/35-practical-examples-of-linux-find-command/

  • find all .txt files and remove them..
    • find . -type f -name "*.txt" -exec rm -f {} \;
  • Find Directories with 777 Permissions and chmod to 755
    • find / -type d -perm 777 -print -exec chmod 755 {} \;
  • find / -type f ! -perm 777 - files without having 777 permissions
  • Find Last 50 Days Modified Files - find / -mtime 50
  • Find Last 50 Days Accessed Files - find / -atime 50
  • 50 to 100 - find / -mtime +50 –mtime -100
  • find / -mmin -60 - modified in last
    • accessed - find / -amin -60

• man → manual

• mv [source_directory] [destination_directory] - also works for files..

• cp -r [source_directory] [destination_directory] - just remove -r to work with files

Commands List

[server@epam .ssh]$ sudo netstat -tunlp | grep “:80” tcp6 0 0 :::80 :::* LISTEN 6216/httpd

[server@epam .ssh]$ sudo netstat -tunlp | grep “:22” tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 5833/sshd: /usr/sbi tcp6 0 0 :::22 :::* LISTEN 5833/sshd: /usr/sbi

Command	Logic / One-Line Working
netstat -tunlp	Shows TCP, UDP, Numeric IPs, Listening ports, and PIDs.
ss -atp	Lists all active TCP connections and the programs using them.
ss -ntlp	grep :80`
netstat -rn	Displays the Kernel Routing Table (shows your gateway).
ss -s	Displays a summary of socket statistics (how many established, closed, etc.).
netstat -i	Displays a table of all Network Interfaces and error/packet counts.

Command	One-Line Working
tcpdump -i eth0	Captures all traffic flowing through the eth0 interface.
tcpdump -c 5 -i any	Captures exactly 5 packets from all interfaces and then exits.
tcpdump -n -i any	Disables DNS resolution to show raw IP addresses instead of hostnames.
tcpdump port 22	Filters and shows only traffic related to SSH.
tcpdump src 10.0.0.10w	Captures only packets coming from the specific IP 10.0.0.10.
tcpdump -w capture.pcap	Saves the captured traffic to a file to be opened later in Wireshark.
tcpdump -A -i any	Prints the packet content in ASCII (useful for reading HTTP/unencrypted data).
tcpdump icmp	Filters and shows only Ping (ICMP) traffic.

Category	Command	Purpose
Monitoring/Info	lsblk	List block devices and their tree structure.
	pvs / vgs / lvs	Quick summary of PVs, VGs, or LVs.
	pvdisplay / vgdisplay / lvdisplay	Detailed metadata for PVs, VGs, or LVs.
	watch -n 2 df -h	Continuously monitor disk space every 2 seconds.
	blkid <path>	Get the UUID of a block device (needed for fstab).
Physical Volumes	pvcreate <disk>	Initialize disk for LVM use.
	pvremove <disk>	Wipe LVM metadata from a disk.
Volume Groups	vgcreate <name> <pv>	Create a new pool from physical volume(s).
	vgextend <name> <pv>	Add a new physical disk to an existing pool.
	vgremove <name>	Delete a volume group.
Logical Volumes	lvcreate -L 5G -n <name> <vg>	Create a new logical volume.
	lvextend -L +5G <lv_path>	Increase LV size by 5GB.
	lvextend -l +100%FREE <lv> -r	Use all free VG space AND automatically resize filesystem.
	lvreduce -L 5G <lv_path>	Shrink LV size to 5GB (Shrink FS first!).
	lvchange -an <lv> / -ay <lv>	Deactivate (-an) or Activate (-ay) an LV.
	lvremove <lv_path>	Delete a logical volume.
Filesystems	mkfs.ext4 <lv_path>	Format the LV with the ext4 filesystem.
	mount <lv_path> <mount_dir>	Mount the filesystem to a directory.
	umount <mount_dir>	Unmount the filesystem.
	mount -a	Test /etc/fstab configuration to ensure safe reboots.
	resize2fs <lv_path>	Expand/shrink ext4 filesystem to match LV size.
	e2fsck -f <lv_path>	Force check filesystem for errors (required before shrinking).
Snapshots	lvcreate -s -L 1G -n <name> <lv>	Create a 1GB point-in-time snapshot.
	lvconvert --merge <snap_path>	Rollback the original LV to the snapshot’s state.
Testing/Utils	cat /dev/zero > <file>	Fill a file with zeros to test 100% disk usage.
	truncate -s 0 <file>	Empty a file instantly to free space.
	apt clean	Clear local package cache to free emergency space.