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Filesystems

Chapter 11: Linux File Systems

Section titled “Chapter 11: Linux File Systems”

Overview

Section titled “Overview”

This chapter covers Linux file systems - types, characteristics, and how to choose the right one for your needs.

11.1 File System Types

Section titled “11.1 File System Types”

Common Linux File Systems

Section titled “Common Linux File Systems”

Linux supports numerous file systems, each with different characteristics and use cases.

+------------------------------------------------------------------+
|                    Linux File System Types                          |
+------------------------------------------------------------------+


                        File Systems
                              |
        +---------------------+---------------------+
        |                     |                     |
        v                     v                     v
  +----------+          +----------+          +----------+
  | Native   |          | Journaling|          | Network  |
  | Linux FS |          |   FS     |          |   FS     |
  +----------+          +----------+          +----------+
       |                    |                    |
       v                    v                    v
  +----------+          +----------+          +----------+
  | ext2     |          | ext3     |          | NFS     |
  | ext4     |          | ext4     |          | CIFS/SMB|
  | btrfs    |          | xfs      |          | sshfs   |
  | xfs      |          | jfs      |          |         |
  | jfs      |          | reiserfs |          |         |
  +----------+          +----------+          +----------+

Local File Systems

Section titled “Local File Systems”
File SystemTypeJournalMax File SizeMax Volume
ext2NativeNo2TB4TB
ext3NativeYes2TB4TB
ext4NativeYes16TB1EB
xfsNativeYes8EB8EB
btrfsNativeYes16EB16EB
jfsNativeYes8PB8PB
reiserfsNativeYes8TB16TB

Network File Systems

Section titled “Network File Systems”
File SystemProtocolUse Case
NFSTCP/UDPUnix/Linux file sharing
CIFS/SMBSMBWindows file sharing
sshfsSSHSecure remote mounting

Btrfs Features

Section titled “Btrfs Features”
+------------------------------------------------------------------+
|                      Btrfs Features                                 |
+------------------------------------------------------------------+


                         +-------------+
                         |    Btrfs    |
                         |  (Modern)   |
                         +-------------+
                               |
         +---------------------+---------------------+
         |                     |                     |
         v                     v                     v
   +----------+          +----------+          +----------+
   | Snapshots|          |  Copy on |          |  Data    |
   | & Clones |          |  Write   |          |  Compression |
   +----------+          +----------+          +----------+
         |                     |                     |
         +---------------------+---------------------+
                               |
         +---------------------+---------------------+
         |                     |                     |
         v                     v                     v
   +----------+          +----------+          +----------+
   |  RAID    |          |  Online  |          |  Subvolumes |
   | Support  |          |  FS Check|          |   & Quotas |
   +----------+          +----------+          +----------+


+------------------------------------------------------------------+
| Feature              | Description                                 |
+----------------------+---------------------------------------------+
| Snapshots           | Point-in-time copies of filesystem          |
| Copy-on-Write       | Efficient cloning, no data duplication     |
| Compression        | Transparent zstd/zlib compression           |
| RAID Support       | Native RAID 0,1,5,6,10 support              |
| Online FS Check   | fsck while mounted (scrub)                  |
| Subvolumes        | Separate mountable filesystem trees         |
| Quotas            | Group-based quota support                   |
| Deduplication     | Block-level deduplication (optional)        |
| Encryption        | Native fs-level encryption (experimental)    |
+----------------------+--------------------------------------------+

Choosing a File System

Section titled “Choosing a File System”
+------------------------------------------------------------------+
|                 File System Selection Guide                         |
+------------------------------------------------------------------+


  Workload Type              Recommended FS    Reason
  +----------------------+   +-------------+  +-------------------+
  | General purpose      |   | ext4        |  | Widely supported  |
  +----------------------+   +-------------+  +-------------------+
  | Large files/db      |   | xfs         |  | High performance  |
  +----------------------+   +-------------+  +-------------------+
  | Modern features     |   | btrfs       |  | Snapshots, etc   |
  +----------------------+   +-------------+  +-------------------+
  | Network sharing     |   | nfs         |  | Standard protocol |
  +----------------------+   +-------------+  +-------------------+
  | Windows sharing     |   | cifs/smb    |  | Native to Windows |
  +----------------------+   +-------------+  +-------------------+
  • ext4: Best for general purpose use, widely supported
  • xfs: Excellent for large files and high-performance workloads
  • btrfs: Modern features like snapshots, compression, deduplication
  • xfs: Ideal for databases and large file storage
  • NFS: Network file sharing in enterprise environments

11.2 Creating and Managing File Systems

Section titled “11.2 Creating and Managing File Systems”

Creating File Systems

Section titled “Creating File Systems”
+------------------------------------------------------------------+
|                 Creating File Systems                               |
+------------------------------------------------------------------+


  Physical Disk              Format                   Mount
  +----------+            +----------+            +----------+
  | /dev/sdb1|---------->| mkfs.ext4|---------->| /mnt/data|
  +----------+            +----------+            +----------+


  Commands:
  +----------------------------------------------------------+
  | mkfs.ext4 /dev/sdb1        - Create ext4 FS             |
  | mkfs.xfs /dev/sdb1         - Create xfs FS              |
  | mkfs.btrfs /dev/sdb1       - Create btrfs FS           |
  | mkfs.ext4 -L "data" /dev/sdb1 - With label             |
  +----------------------------------------------------------+
Terminal window
# Create ext4 file system
mkfs.ext4 /dev/sdb1


# Create xfs file system
mkfs.xfs /dev/sdb1


# Create btrfs file system
mkfs.btrfs /dev/sdb1


# With specific options
mkfs.ext4 -L "data" -m 0 /dev/sdb1

Checking File Systems

Section titled “Checking File Systems”
Terminal window
# Check ext file system (read-only recommended)
fsck.ext4 /dev/sdb1


# Check xfs file system
xfs_repair /dev/sdb1


# Check btrfs file system
btrfs check /dev/sdb1

Mounting File Systems

Section titled “Mounting File Systems”
+------------------------------------------------------------------+
|                    Mount Process                                    |
+------------------------------------------------------------------+


  Device                 Mount Point           File System
  +--------+            +----------+          +----------+
  |/dev/sdb1| -------->| /mnt/data| -------->| ext4     |
  +--------+            +----------+          +----------+


  Options: rw, ro, noexec, nosuid, nodev, sync, async
Terminal window
# Mount temporarily
mount /dev/sdb1 /mnt/data


# Mount with specific options
mount -o rw,noexec,nosuid /dev/sdb1 /mnt/data


# View mount options
mount | grep /dev/sdb1


# Unmount
umount /mnt/data

Persistent Mounts (/etc/fstab)

Section titled “Persistent Mounts (/etc/fstab)”
# <file system>           <mount point>   <type>  <options>    <dump> <pass>
/dev/sdb1                 /mnt/data       ext4    defaults      0      2
LABEL=data                /mnt/data       ext4    defaults      0      2
UUID=xxxxxxxx-xxxx-xxxx  /mnt/data       ext4    defaults      0      2


+----------------------------------------------------------+
| Options:                                                 |
| defaults  = rw, suid, dev, exec, auto, nouser, async   |
| noauto    = Don't mount at boot                         |
| user      = Allow user to mount                         |
| noexec    = No executables allowed                      |
| nosuid    = Ignore suid/sgid bits                      |
+----------------------------------------------------------+

11.3 Disk Quotas

Section titled “11.3 Disk Quotas”

Setting Up Quotas

Section titled “Setting Up Quotas”
+------------------------------------------------------------------+
|                    Setting Up Quotas                               |
+------------------------------------------------------------------+


  Step 1: Enable in /etc/fstab
  +----------------------------------------------------------+
  | /dev/sdb1   /mnt/data   ext4   defaults,usrquota,grpquota |
  +----------------------------------------------------------+


  Step 2: Remount
  +----------------------------------------------------------+
  | mount -o remount /mnt/data                               |
  +----------------------------------------------------------+


  Step 3: Create quota files
  +----------------------------------------------------------+
  | quotacheck -cug /mnt/data                               |
  +----------------------------------------------------------+


  Step 4: Enable quotas
  +----------------------------------------------------------+
  | quotaon /mnt/data                                       |
  +----------------------------------------------------------+
Terminal window
# Install quota tools
apt-get install quota
yum install quota


# Enable quotas in /etc/fstab
/dev/sdb1    /mnt/data    ext4    defaults,usrquota,grpquota    0    2


# Remount filesystem
mount -o remount /mnt/data


# Create quota files
quotacheck -cug /mnt/data


# Enable quotas
quotaon /mnt/data

Managing User Quotas

Section titled “Managing User Quotas”
Terminal window
# Set user quota
edquota -u username


# Set group quota
edquota -g groupname


# View user quota
quota -u username


# Check quota usage
repquota -a

11.4 Disk Usage Analysis

Section titled “11.4 Disk Usage Analysis”

du Command

Section titled “du Command”
+------------------------------------------------------------------+
|                    Disk Usage Analysis                              |
+------------------------------------------------------------------+


  du -sh /home           = Show total size of /home
  du -h /home            = Show all directories with sizes
  du -h /home | sort -rh = Sort by size (largest first)
  du -shc /home/*        = Show each item + total


  Example Output:
  +----------------------------------------------------------+
  | 4.0G    /home/user/documents                             |
  | 2.1G    /home/user/downloads                             |
  | 1.5G    /home/user/images                                |
  | 512M    /home/user/videos                                |
  +----------------------------------------------------------+
Terminal window
# Directory size summary
du -sh /home


# All directories with sizes
du -h /home


# Sorted by size
du -h /home | sort -rh


# Total disk usage
du -shc /home/*

df Command

Section titled “df Command”
Terminal window
# Human readable
df -h


# File system type
df -Th


# Inode information
df -i

11.5 LVM (Logical Volume Manager)

Section titled “11.5 LVM (Logical Volume Manager)”

LVM Architecture

Section titled “LVM Architecture”
+------------------------------------------------------------------+
|                    LVM Architecture                                |
+------------------------------------------------------------------+


  Physical Disks           Physical Volumes      Volume Groups
  +----------+           +------------+        +--------------+
  | /dev/sdb | -------->| pvcreate   | ------>| vgcreate     |
  | /dev/sdc |           | /dev/sdb1  |        | vg_data      |
  +----------+           +------------+        +--------------+


                              |                       |
                              v                       v
                        +------------+        +--------------+
                        | pvs        |        | lvs          |
                        | pvdisplay |        | lvcreate     |
                        +------------+        +--------------+
                                                    |
                                                    v
                                              +--------------+
                                              | /dev/mapper/ |
                                              | vg_data-     |
                                              | lv_data      |
                                              +--------------+

Basic LVM Commands

Section titled “Basic LVM Commands”
Terminal window
# Physical Volume
pvcreate /dev/sdb1
pvdisplay /dev/sdb1
pvs


# Volume Group
vgcreate vg_data /dev/sdb1
vgdisplay vg_data
vgs


# Logical Volume
lvcreate -L 10G -n lv_data vg_data
lvdisplay /dev/vg_data/lv_data
lvs

LVM Operations

Section titled “LVM Operations”
+------------------------------------------------------------------+
|                    LVM Operations                                  |
+------------------------------------------------------------------+


  Extend Volume Group          Extend Logical Volume
  +-------------------+        +-----------------------+
  | vgextend vg_data |        | lvextend -L +5G      |
  | /dev/sdc1        |        | /dev/vg_data/lv_data|
  +-------------------+        +-----------------------+
                                             |
                                             v
                                    +-----------------------+
                                    | resize2fs            |
                                    | /dev/vg_data/lv_data|
                                    +-----------------------+


  Create Snapshot              Remove Snapshot
  +-------------------+        +-------------------+
  | lvcreate -L 1G   |        | lvremove          |
  | -s -n snap       |        | /dev/vg_data/snap|
  | /dev/vg_data/lv |        +-------------------+
  +-------------------+
Terminal window
# Extend Volume Group
vgextend vg_data /dev/sdc1


# Extend Logical Volume
lvextend -L +5G /dev/vg_data/lv_data
resize2fs /dev/vg_data/lv_data


# Reduce Logical Volume
umount /mnt/data
e2fsck -f /dev/vg_data/lv_data
resize2fs /dev/vg_data/lv_data 5G
lvreduce -L 5G /dev/vg_data/lv_data
mount /mnt/data


# Create snapshot
lvcreate -L 1G -s -n snap_data /dev/vg_data/lv_data

11.6 File System Encryption

Section titled “11.6 File System Encryption”

LUKS (Linux Unified Key Setup)

Section titled “LUKS (Linux Unified Key Setup)”
+------------------------------------------------------------------+
|                    LUKS Encryption Flow                            |
+------------------------------------------------------------------+


  Encrypted          Opened              Mounted
  Container          Container           Filesystem
  +----------+       +----------+        +----------+
  | /dev/sdb1|-------->| luksOpen|-------->| /dev/    |
  | (encrypted)       | cryptsetup|       | mapper   |
  +----------+       +----------+        +----------+
                          |
                          v
                     +----------+
                     | Keyslot  |
                     | (pasword)|
                     +----------+
Terminal window
# Create encrypted container
cryptsetup luksFormat /dev/sdb1


# Open encrypted container
cryptsetup luksOpen /dev/sdb1 encrypted_data


# Create file system
mkfs.ext4 /dev/mapper/encrypted_data


# Mount
mount /dev/mapper/encrypted_data /mnt/data


# Close
umount /mnt/data
cryptsetup luksClose encrypted_data

11.7 Troubleshooting

Section titled “11.7 Troubleshooting”

Common Issues

Section titled “Common Issues”
+------------------------------------------------------------------+
|                 Troubleshooting Guide                               |
+------------------------------------------------------------------+


  Problem                 Diagnosis              Solution
  +------------------+  +------------------+   +----------------+
  | Filesystem Full |  | df -h            |   | du -sh /*     |
  +------------------+  +------------------+   +----------------+


  +------------------+  +------------------+   +----------------+
  | Inode Exhaustion|  | df -i            |   | Find & delete |
  +------------------+  +------------------+   +----------------+


  +------------------+  +------------------+   +----------------+
  | Corrupted FS    |  | fsck.ext4        |   | Backup & format|
  +------------------+  +------------------+   +----------------+


  +------------------+  +------------------+   +----------------+
  | Mount Fails     |  | dmesg | tail     |   | Check device   |
  +------------------+  +------------------+   +----------------+

  1. Filesystem Full

    Terminal window
    df -h  # Check usage
    du -sh /*  # Find large directories

  2. Inode Exhaustion

    Terminal window
    df -i  # Check inode usage
    find / -type f | wc -l  # Count files

  3. Corrupted Filesystem

    Terminal window
    # Always unmount first
    umount /dev/sdb1
    

    # Check and repair
    fsck.ext4 -fy /dev/sdb1

  4. Mount Failures

    Terminal window
    # Check device
    fdisk -l
    

    # Check filesystem
    file -s /dev/sdb1
    

    # Check mount options
    dmesg | tail

11.8 Best Practices

Section titled “11.8 Best Practices”
+------------------------------------------------------------------+
|                    Best Practices Checklist                        |
+------------------------------------------------------------------+


  [ ] Always backup before formatting
  [ ] Use appropriate file system for workload
  [ ] Monitor disk usage regularly
  [ ] Enable and configure quotas in multi-user environments
  [ ] Use LVM for flexibility in storage management
  [ ] Implement encryption for sensitive data
  [ ] Schedule regular filesystem checks
  [ ] Keep spare disk space available (10-20%)


  Monitoring Commands:
  +----------------------------------------------------------+
  | df -h           | Disk space usage                      |
  | du -sh          | Directory size                         |
  | df -i           | Inode usage                            |
  | smartctl        | Disk health                           |
  +----------------------------------------------------------+
  1. Always backup before formatting
  2. Use appropriate file system for workload
  3. Monitor disk usage regularly
  4. Enable and configure quotas in multi-user environments
  5. Use LVM for flexibility in storage management
  6. Implement encryption for sensitive data
  7. Schedule regular filesystem checks
  8. Keep spare disk space available (10-20%)

Quick Reference

Section titled “Quick Reference”
+------------------------------------------------------------------+
|                    Quick Reference                                 |
+------------------------------------------------------------------+


  File System Commands:
  +----------------------------------------------------------+
  | mkfs.ext4 /dev/sdb1       | Create ext4 FS             |
  | fsck.ext4 /dev/sdb1       | Check/repair ext4          |
  | mount /dev/sdb1 /mnt/data | Mount filesystem           |
  | umount /mnt/data         | Unmount                    |
  | df -h                    | Show disk usage            |
  | du -sh /dir              | Directory size             |
  +----------------------------------------------------------+


  LVM Commands:
  +----------------------------------------------------------+
  | pvcreate /dev/sdb1          | Create PV                |
  | vgcreate vg_name /dev/sdb1| Create VG                |
  | lvcreate -L 10G -n lv_name | Create LV                |
  | lvextend -L +5G /dev/vg/lv | Extend LV               |
  +----------------------------------------------------------+


  Quota Commands:
  +----------------------------------------------------------+
  | edquota -u user             | Edit user quota         |
  | quota -u user               | View user quota         |
  | repquota -a                 | Report all quotas       |
  +----------------------------------------------------------+