Summary of Linux File Directories, Disk File Systems, and Compression Commands

File and Directory Management

Basic Commands

• • ls – List directory contents

  ls              # List files and directories in the current directory
  ls -l           # Long format to display detailed information
  ls -a           # Show all files (including hidden files)
  ls -la          # Show detailed information and hidden files

• • cd – Change working directory

  cd /path/to/directory   # Switch to the specified directory
  cd ..                  # Go back to the parent directory
  cd ~                   # Switch to the user's home directory

• • pwd – Display current working directory

  pwd                    # Print the full path of the current working directory

• • mkdir – Create a new directory

  mkdir directory_name    # Create a new directory named directory_name
  mkdir -p path/to/directory  # Recursively create necessary parent directories

• • rmdir – Remove empty directories

  rmdir directory_name    # Remove the empty directory named directory_name
  rmdir -p path/to/directory  # Recursively remove empty directories

• • cp – Copy files or directories

  cp file1 file2         # Copy file1 to file2
  cp -R /source_directory /destination_directory  # Recursively copy an entire directory

• • mv – Move or rename files or directories

  mv old_name new_name   # Rename file or directory
  mv /source/file /destination/  # Move file to another location

• • rm – Remove files or directories

  rm file_name           # Remove the specified file
  rm -r directory_name   # Recursively remove a directory and its contents
  rm -i file_name        # Prompt for confirmation before deletion

• • touch – Update file timestamp or create an empty file

  touch file_name        # If the file exists, update its access and modification times; if it does not exist, create an empty file

File Compression and Decompression

Basic Commands

• • gzip – Compress files

  gzip file_name         # Compress the file, generating file_name.gz

• • gunzip – Decompress files

  gunzip file_name.gz    # Decompress file_name.gz, restoring it to the original file

• • tar – Archiving tool that supports compression

  tar -cvf archive.tar file1 file2  # Create archive file archive.tar
  tar -xvf archive.tar               # Extract archive file archive.tar
  tar -zcvf archive.tar.gz file1     # Create archive file archive.tar.gz using gzip compression
  tar -zxvf archive.tar.gz           # Decompress gzip compressed archive file
  tar -jcvf archive.tar.bz2 file1    # Create archive file archive.tar.bz2 using bzip2 compression
  tar -jxvf archive.tar.bz2          # Decompress bzip2 compressed archive file

• • zip/unzip – Compress/Decompress .zip files

  zip archive.zip file1 file2       # Compress files into archive.zip
  unzip archive.zip                 # Decompress .zip file

Basic Permissions

In Linux, file and directory permissions are divided into three categories: read (r), write (w), and execute (x), corresponding to the values 4, 2, and 1, respectively. Permissions can be assigned to three groups of users: owner (u), group (g), and others (o).

Basic Permission Commands

chmod – Change file mode

• • Symbolic Mode

  chmod u+x,g+w,o-r file.txt  # Add execute permission for the file owner, write permission for the group, and remove read permission for others
  chmod a+r file.txt          # Add read permission for all users

• • Absolute Mode

  chmod 755 directory         # Set directory permissions to rwxr-xr-x
  chmod 644 file.txt          # Set file permissions to rw-r--r--

chown – Change file owner and group

• • Change the owner of a file

  sudo chown newowner file.txt   # Change the owner of file.txt to newowner

• • Change the owner and group of a file

  sudo chown newowner:newgroup file.txt  # Change both owner and group

chgrp – Change file group

• • Change the group of a file

  sudo chgrp newgroup file.txt   # Change the group of file.txt to newgroup

Special Permissions

SUID, SGID, and Sticky Bit

• • SUID (Set User ID)

  chmod u+s /path/to/program    # Set the SUID bit

• • SGID (Set Group ID)

  chmod g+s /path/to/directory  # Set the SGID bit

• • Sticky Bit

  chmod +t /path/to/directory   # Set the sticky bit, usually for shared directories

ACLs (Access Control Lists)

ACLs provide a more granular way of managing permissions.

Setting ACL

• • Set user ACL

  setfacl -m u:username:rwx file.txt  # Set rwx permissions for a specific user

• • Set default ACL

  setfacl -d -m u:username:rwx directory  # Set default permissions for new files and directories

View ACL

• • Use<span>getfacl</span> command to view ACL information

  getfacl file.txt  # Display the ACL settings of file.txt

Useful Tips

• • umask – Set the default permission mask for newly created files and directories

  umask                    # View the current umask value
  umask 022               # Set the umask value, affecting the default permissions for subsequent file creation

Disk and File System Management

Basic Commands

• • df – Display disk space usage

  df                     # Show disk usage for each mounted file system
  df -h                  # Display in a more readable format

• • du – Display disk usage of directories or files

  du                     # Show disk usage for each file and directory
  du -sh directory_name  # Show total size of the specified directory

• • fdisk – Partition table manipulation tool

  sudo fdisk -l          # List all partition tables

• • mount – Mount file systems

  mount /dev/sdb1 /mnt   # Mount device /dev/sdb1 to /mnt

• • umount – Unmount file systems

  umount /mnt            # Unmount the file system on /mnt

Software RAID Basics

In Linux, software RAID can be created and managed using the<span>mdadm</span> tool. Here are some commonly used commands and their usage examples.

Install mdadm

First, ensure that mdadm is installed on the system. If it is not installed, you can use the following commands to install it:

• • Debian/Ubuntu

  sudo apt-get install mdadm

• • CentOS/RHEL

  sudo yum install mdadm

Create RAID Arrays

Create RAID 0 (Striping)

Assuming we have two disks /dev/sdb and /dev/sdc, to create a RAID 0 array:

sudo mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb /dev/sdc

Create RAID 1 (Mirroring)

To create a RAID 1 array, also using the two disks /dev/sdb and /dev/sdc:

sudo mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc

Create RAID 5

For RAID 5, at least three disks are required:

sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sd[b-d]

Manage RAID Arrays

View RAID Status

To view the status of all RAID devices:

cat /proc/mdstat

Or use<span>mdadm</span>:

sudo mdadm --detail /dev/md0

Stop RAID Arrays

To stop a specific RAID device (e.g., /dev/md0):

sudo mdadm --stop /dev/md0

Delete RAID Arrays

Before deleting, stop the array first, then you can remove the superblock:

sudo mdadm --zero-superblock /dev/sdX

Here,<span>/dev/sdX</span> represents one of the physical disks involved in the RAID.

Configuration and Maintenance

Update Configuration File

After creating or modifying a RAID, it is recommended to update the<span>/etc/mdadm.conf</span> file so that the RAID configuration can be automatically loaded on system reboot:

sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf

Monitor RAID Health

You can monitor RAID health status by setting up email notifications:

Edit<span>/etc/mdadm.conf</span>, adding or modifying the following line:

MAILADDR [email protected]

Then restart the<span>mdmonitor</span> service (if it exists):

sudo systemctl restart mdmonitor

LVM (Logical Volume Management)

pvcreate – Create Physical Volume

• • Create a physical volume:

  sudo pvcreate /dev/sdX1

vgcreate – Create Volume Group

• • Create a volume group:

  sudo vgcreate myvg /dev/sdX1 /dev/sdY1

lvcreate – Create Logical Volume

• • Create a logical volume:

  sudo lvcreate -L 10G -n mylv myvg

lvextend – Extend Logical Volume

• • Extend the size of a logical volume:

  sudo lvextend -L +10G /dev/myvg/mylv

• • Use resize2fs to adjust the file system size (for ext file systems):

  sudo resize2fs /dev/myvg/mylv

Disk Quotas

Enable Quotas

• • Modify the /etc/fstab file to add usrquota and grpquota options for the file system where quotas need to be enabled:

  UUID=xxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /data ext4 defaults,usrquota,grpquota 0 2

• • Remount the file system to make the changes effective:

  sudo mount -o remount /data

Set Quotas

• • Create a quota database file:

  sudo quotacheck -cugm /data

• • Edit user or group quotas:

  sudo edquota -u username
  sudo edquota -g groupname