Linux Directory Structure Explained: A Guide for New System Administrators

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Network engineers transitioning to Linux administration often struggle with directory navigation. Unlike Windows with its drive letters (C:\, D:\), Linux uses a single hierarchical tree structure starting from the root directory (/).

The Linux directory structure follows the Filesystem Hierarchy Standard (FHS). This standard ensures consistency across different Linux distributions. Understanding this structure is essential for:

System configuration management
Troubleshooting network services
Security hardening
Performance optimization
Backup and recovery operations

This guide provides a complete roadmap for mastering Linux directories. You will learn directory purposes, common use cases, and practical examples relevant to network administration.

The Root Directory (/) – Foundation of Linux Directory Structure

What is the Root Directory in Linux?

The root directory (/) is the top-level directory in Linux. All other directories branch from this single point. Do not confuse the root directory (/) with the root user’s home directory (/root).

Key characteristics of the root directory:

Contains all system directories and files
Requires administrative privileges for modifications
Forms the base for absolute paths
Cannot be unmounted while system is running

Navigating from Root: Essential Commands

Master these basic navigation commands:

# Display current directory
pwd

# List root directory contents
ls /

# List with detailed information
ls -la /

# Change to root directory
cd /

# Return to previous directory
cd -

# Go to home directory
cd ~

Absolute vs. Relative Paths:

Absolute path: Starts with / (example: /etc/ssh/sshd_config)
Relative path: Starts from current directory (example: ./scripts/backup.sh)

Essential System Directories Every Linux Administrator Must Know

/bin – Essential User Command Binaries

The /bin directory contains essential command binaries needed for single-user mode and basic system operation.

Common commands in /bin:

ls – List directory contents
cp – Copy files
mv – Move files
rm – Remove files
cat – Display file contents
echo – Display text
grep – Search text patterns
ping – Test network connectivity

# View all binaries in /bin
ls /bin

# Check if a command is in /bin
which ping
# Output: /bin/ping

# Count binaries in /bin
ls /bin | wc -l

/sbin – System Administration Binaries

The /sbin directory contains system administration commands typically requiring root privileges.

Important network-related tools in /sbin:

ifconfig – Configure network interfaces (deprecated)
ip – Modern network configuration tool
iptables – Firewall management
route – Routing table management
systemctl – Service management
fdisk – Disk partitioning

# Configure network interface
sudo /sbin/ip addr add 192.168.1.100/24 dev eth0

# View routing table
sudo /sbin/ip route show

# Manage firewall rules
sudo /sbin/iptables -L -n -v

# Restart network service
sudo /sbin/systemctl restart NetworkManager

/etc – System Configuration Files Directory

The /etc directory stores system-wide configuration files. Network administrators spend significant time working with files in this directory.

Critical network configuration locations:

# Network configuration files
/etc/network/interfaces              # Debian/Ubuntu network config
/etc/sysconfig/network-scripts/      # RedHat/CentOS network config
/etc/netplan/                        # Ubuntu 18.04+ network config
/etc/hosts                           # Static hostname mappings
/etc/resolv.conf                     # DNS resolver configuration
/etc/hostname                        # System hostname

Service configuration examples:

# SSH configuration
/etc/ssh/sshd_config                # SSH server configuration
/etc/ssh/ssh_config                 # SSH client configuration

# Apache web server
/etc/apache2/apache2.conf           # Main Apache config (Debian)
/etc/httpd/conf/httpd.conf          # Main Apache config (RedHat)

# Nginx configuration
/etc/nginx/nginx.conf               # Main Nginx configuration
/etc/nginx/sites-available/         # Available site configurations
/etc/nginx/sites-enabled/           # Enabled site configurations

Example: Configure static IP on Ubuntu 20.04 using Netplan:

# Edit Netplan configuration
sudo nano /etc/netplan/00-installer-config.yaml

# Configuration content:
network:
  version: 2
  ethernets:
    eth0:
      addresses:
        - 192.168.1.100/24
      gateway4: 192.168.1.1
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4

# Apply configuration
sudo netplan apply

/var – Variable Data Files in Linux

The /var directory contains variable data that changes during system operation.

Important subdirectories:

/var/log/ – System and application logs
/var/cache/ – Application cache data
/var/spool/ – Print and mail queues
/var/lib/ – Variable state information
/var/www/ – Web server document root (common location)
/var/tmp/ – Temporary files preserved between reboots

Log file locations for troubleshooting:

# System logs
/var/log/syslog                     # System messages (Debian/Ubuntu)
/var/log/messages                   # System messages (RedHat/CentOS)
/var/log/auth.log                   # Authentication logs
/var/log/kern.log                   # Kernel logs

# Service-specific logs
/var/log/apache2/access.log         # Apache access log
/var/log/apache2/error.log          # Apache error log
/var/log/nginx/access.log           # Nginx access log
/var/log/nginx/error.log            # Nginx error log
/var/log/mysql/error.log            # MySQL error log

# Network service logs
/var/log/secure                     # SSH login attempts (RedHat)
/var/log/auth.log                   # SSH login attempts (Debian)

Monitor logs in real-time:

# Follow system log
tail -f /var/log/syslog

# Monitor SSH authentication
tail -f /var/log/auth.log | grep sshd

# Watch Apache access log
tail -f /var/log/apache2/access.log

# Check disk usage in /var
du -sh /var/*
df -h /var

User and Application Directories in Linux Systems

/home – User Home Directories

The /home directory contains personal directories for regular users. Each user gets a subdirectory matching their username.

Home directory structure:

/home/
├── user1/
│   ├── .bashrc              # Bash configuration
│   ├── .profile             # Shell profile
│   ├── .ssh/                # SSH keys and config
│   │   ├── authorized_keys  # Public keys for SSH access
│   │   ├── id_rsa          # Private SSH key
│   │   └── id_rsa.pub      # Public SSH key
│   ├── Documents/
│   ├── Downloads/
│   └── Scripts/
└── user2/

Managing user home directories:

# Create new user with home directory
sudo useradd -m -s /bin/bash newuser

# Set permissions for home directory
sudo chmod 755 /home/newuser

# Set disk quota for user
sudo setquota -u newuser 1000000 1500000 0 0 /home

# Generate SSH keys for user
su - newuser
ssh-keygen -t rsa -b 4096 -C "newuser@example.com"

/root – System Administrator Home Directory

The /root directory is the home directory for the root user. Unlike regular users, root’s home is not under /home.

Security considerations for /root:

Restricted permissions (typically 700)
Contains sensitive administrative scripts
Stores root’s SSH keys
Should not be accessible to regular users

# Check /root permissions
ls -ld /root
# Output: drwx------ root root /root

# Access root's home directory
sudo su -
cd ~
pwd
# Output: /root

/usr – User System Resources

The /usr directory contains user utilities and applications. Modern Linux systems merge /bin with /usr/bin through symbolic links.

Important /usr subdirectories:

/usr/
├── bin/        # User commands
├── sbin/       # System administration commands
├── local/      # Locally installed software
│   ├── bin/
│   ├── sbin/
│   └── share/
├── lib/        # Libraries for /usr/bin and /usr/sbin
├── share/      # Architecture-independent data
│   ├── doc/    # Documentation
│   └── man/    # Manual pages
└── src/        # Source code (often kernel sources)

Installing custom software in /usr/local:

# Compile and install software from source
cd /tmp
wget https://example.com/software.tar.gz
tar -xzf software.tar.gz
cd software/
./configure --prefix=/usr/local
make
sudo make install

# Add /usr/local/bin to PATH
echo 'export PATH=$PATH:/usr/local/bin' >> ~/.bashrc
source ~/.bashrc

/opt – Optional Application Software

The /opt directory stores self-contained third-party applications.

Common applications in /opt:

Google Chrome (/opt/google/chrome)
Slack (/opt/slack)
Custom enterprise applications
Proprietary software packages

# Example: Install custom application
sudo mkdir /opt/myapp
sudo tar -xzf myapp.tar.gz -C /opt/myapp/

# Create symbolic link for easy access
sudo ln -s /opt/myapp/bin/myapp /usr/local/bin/myapp

# Set permissions
sudo chown -R root:root /opt/myapp
sudo chmod -R 755 /opt/myapp

Critical Runtime and Temporary Directories

/tmp – Temporary File Storage

The /tmp directory stores temporary files. Most systems clear /tmp on reboot.

Security features of /tmp:

Sticky bit enabled (only owner can delete their files)
World-writable permissions
Often mounted as tmpfs (RAM-based filesystem)

# Check /tmp permissions
ls -ld /tmp
# Output: drwxrwxrwt root root /tmp
# Note: 't' indicates sticky bit

# Create temporary file safely
mktemp /tmp/myfile.XXXXXX

# Clean files older than 7 days
find /tmp -type f -atime +7 -delete

# Monitor /tmp usage
watch -n 1 'du -sh /tmp; ls -la /tmp | wc -l'

/dev – Device Files Directory

The /dev directory contains device files representing hardware and virtual devices.

Important device files:

/dev/null      # Null device (discards all data)
/dev/zero      # Produces null bytes
/dev/random    # Random number generator
/dev/urandom   # Non-blocking random generator
/dev/sda       # First SATA drive
/dev/sda1      # First partition of first SATA drive
/dev/tty       # Terminal devices
/dev/pts/      # Pseudo-terminal devices

Network-related devices:

# List network interfaces
ls -la /sys/class/net/

# Create virtual network interface
sudo ip link add veth0 type veth peer name veth1

# View disk devices
lsblk
fdisk -l

/proc – Process Information Pseudo-Filesystem

The /proc directory is a virtual filesystem providing kernel and process information.

Network configuration via /proc:

# Enable IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

# Disable ICMP redirects
echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects

# View network statistics
cat /proc/net/dev

# Check system memory
cat /proc/meminfo

# View CPU information
cat /proc/cpuinfo

# List all network connections
cat /proc/net/tcp
cat /proc/net/udp

Process information:

# Each process has a directory with its PID
ls /proc/1/              # Init process information
cat /proc/1/cmdline      # Command line of process
cat /proc/1/status       # Process status

/sys – Linux System Information Directory

The /sys directory exposes kernel objects and their attributes.

Network interface management:

# View network interface information
ls /sys/class/net/

# Check interface status
cat /sys/class/net/eth0/operstate

# View MAC address
cat /sys/class/net/eth0/address

# Check interface speed
cat /sys/class/net/eth0/speed

# View interface statistics
cat /sys/class/net/eth0/statistics/rx_bytes
cat /sys/class/net/eth0/statistics/tx_bytes

Boot and Mount Directories Explained

/boot – Linux Boot Files Location

The /boot directory contains files needed to boot the system.

Contents of /boot:

/boot/
├── vmlinuz-5.4.0-42-generic    # Linux kernel
├── initrd.img-5.4.0-42-generic # Initial RAM disk
├── config-5.4.0-42-generic     # Kernel configuration
├── System.map-5.4.0-42-generic # Kernel symbol table
└── grub/                        # GRUB bootloader files
    ├── grub.cfg                 # GRUB configuration
    └── fonts/                   # GRUB fonts

Managing boot directory:

# List installed kernels
ls /boot/vmlinuz-*

# Check boot partition usage
df -h /boot

# Remove old kernels (Ubuntu/Debian)
sudo apt autoremove --purge

# Remove old kernels (RedHat/CentOS)
sudo package-cleanup --oldkernels --count=2

# Update GRUB configuration
sudo update-grub  # Debian/Ubuntu
sudo grub2-mkconfig -o /boot/grub2/grub.cfg  # RedHat/CentOS

/mnt and /media – Mount Points for File Systems

These directories serve as mount points for temporary filesystems and removable media.

Differences:

/mnt – Temporary mount point for administrators
/media – Automatic mount point for removable media

Mounting filesystems:

# Mount USB drive
sudo mount /dev/sdb1 /mnt/usb

# Mount network share (NFS)
sudo mount -t nfs 192.168.1.100:/share /mnt/nfs

# Mount Windows share (CIFS)
sudo mount -t cifs //192.168.1.100/share /mnt/windows \
  -o username=user,password=pass

# View mounted filesystems
mount | column -t
df -h

# Unmount filesystem
sudo umount /mnt/usb

# Create persistent mount in /etc/fstab
echo "192.168.1.100:/share /mnt/nfs nfs defaults 0 0" | \
  sudo tee -a /etc/fstab

Advanced Directories for System Administrators

/lib and /lib64 – Shared Libraries

These directories contain shared libraries needed by system binaries.

Library management:

# View library dependencies
ldd /bin/ls

# Find library location
ldconfig -p | grep libssl

# Update library cache
sudo ldconfig

# View loaded libraries for running process
lsof -p $(pidof nginx) | grep lib

# Fix missing library
sudo apt install lib-missing  # Debian/Ubuntu
sudo yum install lib-missing  # RedHat/CentOS

/run – Runtime Variable Data

The /run directory stores runtime data since boot. It uses tmpfs (RAM-based filesystem).

Contents of /run:

/run/
├── systemd/        # Systemd runtime data
├── lock/           # Lock files
├── user/           # User runtime directories
└── *.pid           # Process ID files

# View services PID files
ls /run/*.pid

# Check systemd service status files
ls /run/systemd/system/

/srv – Service Data Directory

The /srv directory contains data for services provided by the system.

Common uses:

/srv/
├── www/            # Web server data
│   ├── example.com/
│   └── test.com/
├── ftp/            # FTP server files
└── git/            # Git repositories

# Configure web server to use /srv/www
# Apache configuration
sudo nano /etc/apache2/sites-available/000-default.conf
# Change DocumentRoot to /srv/www/example.com

# Set appropriate permissions
sudo chown -R www-data:www-data /srv/www
sudo chmod -R 755 /srv/www

Linux Directory Permissions and Security Best Practices

Understanding Directory Permission Structure

Directory permissions control access to files and subdirectories.

Permission meanings for directories:

Read (r): List directory contents
Write (w): Create/delete files in directory
Execute (x): Enter directory

# View directory permissions
ls -ld /var/log
# Output: drwxr-xr-x root root /var/log

# Permission breakdown:
# d = directory
# rwx = owner permissions (read, write, execute)
# r-x = group permissions (read, execute)
# r-x = other permissions (read, execute)

# Set directory permissions
chmod 755 /path/to/directory  # rwxr-xr-x
chmod 700 /path/to/private    # rwx------
chmod 775 /path/to/shared     # rwxrwxr-x

# Set ownership
chown user:group /path/to/directory
chown -R user:group /path/to/directory  # Recursive

Special permissions:

# Set SGID on directory (files inherit group)
chmod g+s /shared/directory

# Set sticky bit (only owner can delete)
chmod +t /tmp/shared

# Combined special permissions
chmod 1755 /tmp/shared  # Sticky bit + 755
chmod 2755 /shared/dir  # SGID + 755

Security Hardening for Critical Directories

Restrict access to sensitive directories:

# Secure configuration directories
chmod 700 /root
chmod 755 /etc
chmod 644 /etc/passwd
chmod 640 /etc/shadow
chmod 600 /etc/ssh/sshd_config

# Audit directory access
auditctl -w /etc/passwd -p wa -k passwd_changes
auditctl -w /var/log -p wa -k log_changes

# View audit logs
ausearch -k passwd_changes

# SELinux context management
ls -Z /var/www/html
restorecon -Rv /var/www/html
semanage fcontext -a -t httpd_sys_content_t "/srv/www(/.*)?"

Practical Directory Management for Network Engineers

Common Directory Operations and Commands

Finding files across directories:

# Find files by name
find / -name "*.conf" 2>/dev/null
find /etc -name "*apache*"

# Find files modified in last 24 hours
find /var/log -mtime -1

# Find large files
find / -size +100M 2>/dev/null

# Locate command (uses database)
sudo updatedb  # Update database
locate sshd_config

# Which command (find executable)
which python3
whereis nginx

Disk usage analysis:

# Check disk usage by directory
du -sh /*
du -sh /var/*
du -h --max-depth=1 /var

# Sort by size
du -sh /* | sort -rh

# Filesystem usage
df -h
df -i  # Inode usage

# Interactive disk usage analyzer
ncdu /var

Directory synchronization:

# Sync directories with rsync
rsync -avz /source/ /destination/
rsync -avz --delete /source/ /destination/

# Backup configuration files
rsync -avz /etc/ /backup/etc/

# Remote sync over SSH
rsync -avz -e ssh /local/dir/ user@remote:/remote/dir/

# Exclude certain files
rsync -avz --exclude='*.log' --exclude='cache/' /source/ /dest/

Network Service Directory Locations

Common network service directories:

# SSH Service
/etc/ssh/                    # Configuration
/var/log/auth.log           # Logs (Debian)
/var/log/secure             # Logs (RedHat)
~/.ssh/                     # User SSH files

# Apache Web Server
/etc/apache2/               # Configuration (Debian)
/etc/httpd/                 # Configuration (RedHat)
/var/www/html/              # Default web root
/var/log/apache2/           # Logs

# Nginx Web Server
/etc/nginx/                 # Configuration
/usr/share/nginx/html/      # Default web root
/var/log/nginx/             # Logs

# MySQL/MariaDB
/etc/mysql/                 # Configuration
/var/lib/mysql/             # Database files
/var/log/mysql/             # Logs

# BIND DNS
/etc/bind/                  # Configuration (Debian)
/etc/named/                 # Configuration (RedHat)
/var/cache/bind/            # Cache files

# Network Manager
/etc/NetworkManager/        # Configuration
/var/lib/NetworkManager/    # State files

Linux Directory Structure Troubleshooting Guide

Common Issues and Solutions

“No space left on device” diagnosis:

# Check disk usage
df -h
df -i  # Check inode usage

# Find large files
find / -size +1G 2>/dev/null

# Find directories consuming space
du -sh /* | sort -rh | head -20

# Clean package cache
sudo apt clean  # Debian/Ubuntu
sudo yum clean all  # RedHat/CentOS

# Clean log files
sudo journalctl --vacuum-time=7d
sudo find /var/log -name "*.log" -mtime +30 -delete

# Clear /tmp safely
sudo find /tmp -type f -atime +7 -delete

Permission denied errors:

# Diagnose permission issues
ls -la /path/to/file
namei -l /path/to/file

# Fix common permission problems
chmod 644 file.txt  # Read for all, write for owner
chmod 755 script.sh  # Executable
chown user:group file.txt

# Check effective permissions
sudo -u username test -r /path/to/file && echo "Can read"
sudo -u username test -w /path/to/file && echo "Can write"
sudo -u username test -x /path/to/file && echo "Can execute"

Missing directory problems:

# Create missing directory structure
mkdir -p /path/to/nested/directory

# Restore default directory structure
mkdir -p /var/log/apache2
chown root:adm /var/log/apache2
chmod 750 /var/log/apache2

# Verify directory exists in script
if [ ! -d "/path/to/directory" ]; then
    mkdir -p /path/to/directory
fi

Performance Optimization

Filesystem optimization strategies:

# Check filesystem type
mount | grep "^/dev"
df -T

# Monitor I/O performance
iostat -x 1
iotop

# Optimize mount options in /etc/fstab
/dev/sda1 / ext4 defaults,noatime 0 1
/dev/sda2 /var ext4 defaults,noatime,nodiratime 0 2

# Separate partitions for better performance
/     20GB   # Root filesystem
/var  50GB   # Logs and variable data
/home 100GB  # User data
/tmp  10GB   # Temporary files

Directory Structure Comparison: Different Linux Distributions

Red Hat/CentOS vs Debian/Ubuntu Differences

Purpose	RedHat/CentOS	Debian/Ubuntu
Network Configuration	/etc/sysconfig/network-scripts/	/etc/network/ or /etc/netplan/
Apache Config	/etc/httpd/	/etc/apache2/
Package Cache	/var/cache/yum/	/var/cache/apt/
System Logs	/var/log/messages	/var/log/syslog
Cron Jobs	/var/spool/cron/	/var/spool/cron/crontabs/

Container and Cloud Considerations

Docker filesystem structure:

# Docker storage locations
/var/lib/docker/
├── containers/     # Container configurations
├── images/         # Image layers
├── volumes/        # Named volumes
└── overlay2/       # Storage driver data

# View Docker storage usage
docker system df

# Clean Docker resources
docker system prune -a

Kubernetes persistent volumes:

# Kubernetes storage paths
/var/lib/kubelet/pods/          # Pod volumes
/var/lib/kubelet/plugins/       # Volume plugins
/etc/kubernetes/                # Cluster configuration

# Cloud-init directories
/var/lib/cloud/                 # Cloud-init data
/etc/cloud/                     # Cloud-init config

Conclusion: Mastering Linux Directory Navigation

Key takeaways for system administrators:

The Linux directory structure follows a logical hierarchy starting from root (/)
System binaries reside in /bin and /sbin directories
Configuration files live in /etc
Variable data including logs stored in /var
User data organized under /home
Temporary files use /tmp and /var/tmp
Device and process information available through /dev and /proc

Quick reference for daily tasks:

Check logs: /var/log/
Modify configurations: /etc/
Find binaries: /bin, /sbin, /usr/bin, /usr/sbin
User files: /home/username/
Temporary space: /tmp

Next steps for deepening Linux expertise:

Practice navigating directories using command line only
Set up a test environment to experiment with permissions
Implement automated backup scripts for critical directories
Learn advanced find and grep commands for efficient searching
Master rsync for directory synchronization
Study SELinux/AppArmor for enhanced security

Appendices

Linux Directory Structure Cheat Sheet

Directory	Purpose	Common Commands
/	Root directory	cd /, ls /
/bin	Essential user binaries	ls, cp, mv, mkdir
/boot	Boot loader files	ls /boot, df -h /boot
/dev	Device files	ls /dev, lsblk
/etc	Configuration files	ls /etc, grep -r “string” /etc
/home	User home directories	cd ~, ls /home
/lib	Shared libraries	ldd, ldconfig
/mnt	Mount point	mount, umount
/opt	Optional software	ls /opt
/proc	Process information	cat /proc/cpuinfo
/root	Root user home	sudo su -, cd /root
/sbin	System binaries	ifconfig, iptables
/tmp	Temporary files	mktemp, find /tmp
/usr	User programs	ls /usr/bin
/var	Variable data	tail -f /var/log/syslog

Hands-On Lab Exercises

Exercise 1: Directory Navigation

# Navigate to root and list contents
cd /
ls -la

# Count directories in root
ls -d */ | wc -l

# Find your current location
pwd

# Navigate to /etc and back to previous directory
cd /etc
cd -

Exercise 2: Permission Management

# Create test directory structure
mkdir -p /tmp/test/{dir1,dir2,dir3}
touch /tmp/test/dir1/file{1..5}.txt

# Set different permissions
chmod 755 /tmp/test/dir1
chmod 700 /tmp/test/dir2
chmod 777 /tmp/test/dir3

# Test access as different user
sudo -u nobody ls /tmp/test/dir1
sudo -u nobody ls /tmp/test/dir2

Exercise 3: Service Configuration

# Backup SSH configuration
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.backup

# View current configuration
grep -v "^#" /etc/ssh/sshd_config | grep -v "^$"

# Monitor SSH logs
tail -f /var/log/auth.log | grep sshd

Frequently Asked Questions (FAQs)

Q: What is the difference between /bin and /usr/bin?

A: Historically, /bin contained essential system binaries needed for single-user mode, while /usr/bin held user commands. Modern Linux distributions often merge these through symbolic links.

Q: Why can’t I delete files in /tmp even with write permission?

A: The /tmp directory has the sticky bit set. Only the file owner, directory owner, or root can delete files, regardless of directory write permissions.

Q: Where should I install custom applications?

A: Use /opt for self-contained third-party applications or /usr/local for software you compile from source.

Q: How do I find which directory is consuming the most disk space?

A: Use the command: du -sh /* | sort -rh | head -10

Q: What is the /proc directory, and is it using disk space?

A: /proc is a virtual filesystem that exists in memory. It provides kernel and process information but uses no disk space.

Q: Should I store web files in /var/www or /srv/www?

A: Both are acceptable. /var/www is traditional, while /srv/www follows FHS recommendations for service data. Choose based on your distribution’s defaults or organizational standards.

Q: How can I quickly find configuration files for a specific service?

A: Use: find /etc -name "*servicename*" 2>/dev/null

Q: What happens to /tmp files after reboot?

A: Most distributions clear /tmp on reboot, but /var/tmp preserves files. Check your system’s configuration in /etc/default/rcS or systemd settings.

Q: Can I move or resize system directories like /var or /home?

A: Yes, but it requires careful planning. Best practice is to use separate partitions or logical volumes that can be resized or moved to different disks.

Q: How do I set up quotas for the /home directory?

A: Install quota tools, edit /etc/fstab to add usrquota and grpquota options, remount the filesystem, create quota database with quotacheck, and set limits with edquota.

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