NIX Filesystems

Topics - NIX Filesystems

“People have different styles: Some are filters and some are pilers. The people who pile things often know exactly where things are, and they’re often just as organized as people who file things” ― Daniel Levitin

Editor Note:

  • The material below was cobbled together for personal use, from attributed sources, and endured some mild look/feel massage.
  • Document Purpose: Conveniently scoped refresher on the listed Linux material.


  • LPIC2 Prep - Linux Academy
  • Photo source by Simon Zhu on Unsplash

System Startup

Knowledge Targets

  • Properly configure and navigate the standard Linux filesystem, including configuring and mounting various filesystem types.

203.1 Operating Linux Filesystem

Displaying Filesystem Mounting Information

Mount cmd List all mounts /etc/mtab - what mount reads Updated everytime something is mount/unmounted

Manual mount/unmount

Howto mount/umount, -f to force fuser command tells processes using fuser ~/Downloads/Projects $ fuser /Users/rmay /Users/rmay: 487 518 647 654 823 1180c 7277c 7279c 23964c 24048 Options to mount RO - remount, ro

Auto mount with /etc/fstab

Mounting in fstab requires a unique id

  • old - lable
  • new - uuid, will nver change, known when device is first detected by system Mount options
  • options
    • nodev - no device files on fs
    • noexec - no exec files allowed on fs (ie security on fs)
    • suid - protect perms from changing
    • auto (defaults)
    • nouser - require root to mount
      • can specify user
      • anyone - “users” Sync
  • Some memory is reserved for buffers/cache
  • Used to flush filesystem buffers. In old days you’d do this before shutdown.
  • Everything is fast enough now. Also journaled FS can recover.

Swap Space

Swapon/swapoff utilities

  • Man - Enable disable files for swapping
  • swapon -s - list all active swap
  • swapon -a - turns off all swap

Systemd mount and automount units

Systemd generates .mount unit files based on systems /etc/fstab, although they can be generated manually.

  • Each mount file is named based on the mount point it controls, ie /mnt/data must be mnt-data.mount.
  • Mandatory:
    • (what) - absolute path of device, file, or other resource to mount.
    • (where) - absolute path of a directory for the mount point
    • (type) - FS type

203.2 Maintaining Linux Filesystem

FS types

Major types, benefits, and creation. FDISK to manage/partition. MKFS to format.

EXT (2-4)

  • ext4. 1 exabyte XFS
  • Non-journaled, high performance. Supports file sizes up to 8 exab.
  • File system size up to 16 eb
  • Good for lots of tiny files, constantly being updated.
  • Heavy load

Change and View EXT3

  • dumpe2fs -h - dump fs info, only superblock info.
  • Tells us things, like inode count (max files supported), journaled or not, etc.
  • tune2fs - Used to change fs options. Example, you could change reserved blocks percent for superuser.
  • debugfs - A cli, you can execute commands
    • You can unmount a fs, use debugfs on it. You can look at detailed stats of a file (ACL, c/a/mtime, links, mode, etc)


Self-Monitoring, Analysis, and Reporting Technology

  • Built into many ATA, IDE, and SCSI-3 HDs
  • Designed to monitor the reliability of the drive
  • Attempts to predict failures
  • Runs self-tests SMARTD
  • Daemon that interacts with the smart functionality on drives
  • Configurable timing on queries 30m
  • Errors logged to syslog
  • Check drive capability - smartctl -i /dev/sda


Zettabyte File System

  • Designed and implemented by Sun
  • Not LVM, has lots of features (raid, etc) BTRFS
  • balance - Reallocates and balances data across the fs
  • convert - Converts from EXT to BTRFS and back
  • btrfstune - tune and on/off features
  • others

203.3 Creating and configuring linux Filesystem options

Creating Swap Files and Partitions

Loopback and mkiofs

Man - The loop device is a block device that maps its data blocks not to a physical device such as a hard disk or optical disk drive, but to the blocks of a regular file in a filesystem or to another block device.

  • This can be useful for example to provide a block device for a filesystem image stored in a file, so that it can be mounted with the mount command.
  • mount -o loop blah.iso /media/mycd


Linux Unified Key Setup

  • Use it to access encrypted drives
  • yum install cryptsetup
  • cryptsetup luksformat /dev/myvol/secret
  • Warns about overwriting, requires a passphrase-key. Don’t lose this key! String value unencrypts.