tmpfs Cheatsheet: RAM-Based Filesystem Operations

tmpfs is a temporary filesystem that stores files in virtual memory (RAM and swap) instead of persistent storage. This makes it extremely fast for read/write operations but means data is lost when the system reboots. This cheatsheet covers essential tmpfs operations for Linux system administrators and developers.

Understanding tmpfs

tmpfs creates a virtual filesystem that appears as a regular directory but stores all files in memory. It’s particularly useful for:

Temporary file storage requiring high performance
Caching frequently accessed data
Creating secure temporary workspaces
Reducing disk I/O for temporary operations

Essential tmpfs Operations

Mounting tmpfs to Directory

Create and mount a tmpfs filesystem to a directory:

sudo mount -t tmpfs -o size=SIZE tmpfs /path/to/mountpoint

Examples:

# Mount 1GB tmpfs to /tmp/fast
sudo mount -t tmpfs -o size=1G tmpfs /tmp/fast
 
# Mount 512MB tmpfs to /tmp/cache
sudo mount -t tmpfs -o size=512M tmpfs /tmp/cache
 
# Mount tmpfs with specific permissions
sudo mount -t tmpfs -o size=2G,mode=1777 tmpfs /tmp/shared

Listing tmpfs Mounts

View all current tmpfs mounts:

df -h | grep tmpfs

For more detailed information:

mount | grep tmpfs

View tmpfs usage and available space:

df -h /path/to/tmpfs/mount

Advanced tmpfs Configuration

Setting Size Limits

# Percentage of total RAM
sudo mount -t tmpfs -o size=50% tmpfs /tmp/half-ram
 
# Specific size in bytes, KB, MB, or GB
sudo mount -t tmpfs -o size=1073741824 tmpfs /tmp/1gb     # 1GB in bytes
sudo mount -t tmpfs -o size=500M tmpfs /tmp/500mb        # 500MB
sudo mount -t tmpfs -o size=2G tmpfs /tmp/2gb            # 2GB

Permission and Ownership Options

# Set specific permissions (octal notation)
sudo mount -t tmpfs -o size=1G,mode=0755 tmpfs /tmp/restricted
 
# Set user and group ownership
sudo mount -t tmpfs -o size=1G,uid=1000,gid=1000 tmpfs /tmp/userspace
 
# Combine multiple options
sudo mount -t tmpfs -o size=2G,mode=1777,uid=root,gid=root tmpfs /tmp/public

Number of Files and Inodes

# Limit number of files (inodes)
sudo mount -t tmpfs -o size=1G,nr_inodes=1000 tmpfs /tmp/limited-files
 
# Unlimited inodes (default)
sudo mount -t tmpfs -o size=1G,nr_inodes=0 tmpfs /tmp/unlimited

Unmounting tmpfs

# Unmount tmpfs filesystem
sudo umount /path/to/tmpfs/mount
 
# Force unmount if busy
sudo umount -f /path/to/tmpfs/mount
 
# Lazy unmount (unmount when no longer busy)
sudo umount -l /path/to/tmpfs/mount

Persistent tmpfs Configuration

Adding to /etc/fstab

For tmpfs mounts that should persist across reboots:

# Edit /etc/fstab
sudo nano /etc/fstab
 
# Add tmpfs entry
tmpfs /tmp/persistent tmpfs defaults,size=1G,mode=1777 0 0

Common fstab tmpfs entries:

# General purpose tmpfs
tmpfs /tmp/cache tmpfs defaults,size=512M,mode=1777 0 0

# User-specific tmpfs
tmpfs /home/user/tmpfs tmpfs defaults,size=1G,uid=1000,gid=1000,mode=0755 0 0

# System tmpfs with restricted access
tmpfs /var/tmp/system tmpfs defaults,size=2G,mode=0755 0 0

Monitoring tmpfs Usage

Real-time Usage Monitoring

# Watch tmpfs usage in real-time
watch -n 1 'df -h | grep tmpfs'
 
# Monitor specific tmpfs mount
watch -n 1 'df -h /tmp/fast'
 
# Detailed filesystem information
stat -f /path/to/tmpfs/mount

System Memory and tmpfs

# Check system memory usage
free -h
 
# View memory usage including tmpfs
cat /proc/meminfo | grep -E 'MemTotal|MemFree|Shmem'
 
# Check tmpfs usage from /proc/mounts
cat /proc/mounts | grep tmpfs

Performance Optimization

Optimal Size Configuration

Small files: Use smaller tmpfs (100-500MB) for temporary builds
Large operations: Allocate up to 50% of available RAM
System stability: Never exceed 80% of total RAM for all tmpfs combined

Use Cases and Best Practices

Temporary Build Directories

# Create tmpfs for compilation
sudo mount -t tmpfs -o size=2G tmpfs /tmp/build
cd /tmp/build
# Perform build operations
sudo umount /tmp/build

Cache Directories

# Browser cache in tmpfs
sudo mount -t tmpfs -o size=500M tmpfs /home/user/.cache/browser
 
# Application cache
sudo mount -t tmpfs -o size=1G tmpfs /var/cache/app

Troubleshooting Common Issues

tmpfs Full Error

# Check current usage
df -h /path/to/tmpfs
 
# Increase tmpfs size
sudo mount -o remount,size=2G /path/to/tmpfs
 
# Clean up files if needed
sudo rm -rf /path/to/tmpfs/old-files/*

Permission Denied

# Check current permissions
ls -la /path/to/tmpfs
 
# Remount with correct permissions
sudo umount /path/to/tmpfs
sudo mount -t tmpfs -o size=1G,mode=1777 tmpfs /path/to/tmpfs

Mount Point Busy

# Check what's using the mount point
lsof /path/to/tmpfs
fuser -v /path/to/tmpfs
 
# Kill processes using the mount point
sudo fuser -k /path/to/tmpfs
 
# Force unmount
sudo umount -f /path/to/tmpfs

Security Considerations

Secure tmpfs Configuration

# Restricted access tmpfs
sudo mount -t tmpfs -o size=1G,mode=0700,uid=root,gid=root tmpfs /tmp/secure
 
# No execution permissions
sudo mount -t tmpfs -o size=1G,noexec,nosuid,nodev tmpfs /tmp/noexec

Data Protection

Remember that tmpfs data is:

Volatile: Lost on reboot or unmount
Swappable: May be written to swap space
Memory-resident: Visible in memory dumps

For sensitive data, consider:

Using encrypted swap
Implementing proper cleanup procedures
Setting appropriate file permissions

Advanced tmpfs Features

Swap Behavior

# Mount with swap usage control
sudo mount -t tmpfs -o size=1G,nr_inodes=1k tmpfs /tmp/controlled
 
# Check swap usage
swapon -s
cat /proc/swaps

Integration with systemd

Create a systemd service for tmpfs management:

[Unit]
Description=Custom tmpfs mount
Before=local-fs.target
 
[Mount]
What=tmpfs
Where=/tmp/service
Type=tmpfs
Options=size=1G,mode=1777
 
[Install]
WantedBy=multi-user.target

References and Resources

Linux tmpfs Documentation - Official kernel documentation
mount(8) Manual Page - Complete mount command reference
fstab(5) Manual Page - Filesystem table configuration
systemd.mount(5) - systemd mount unit configuration

Questions Answered in This Document

Q: How do I create a tmpfs filesystem in Linux? A: Use sudo mount -t tmpfs -o size=SIZE tmpfs /path/to/mountpoint to create and mount a tmpfs filesystem of specified size to a directory.

Q: What is the difference between tmpfs and regular filesystems? A: tmpfs stores files in RAM/swap instead of disk storage, making it much faster but volatile (data is lost on reboot).

Q: How do I check tmpfs usage and available space? A: Use df -h | grep tmpfs to see all tmpfs mounts and their usage, or df -h /path/to/tmpfs for a specific mount.

Q: Can I make tmpfs mounts persistent across reboots? A: Yes, add tmpfs entries to /etc/fstab with format: tmpfs /mount/point tmpfs defaults,size=1G,mode=1777 0 0.

Q: How do I set size limits for tmpfs? A: Use the size option: size=1G for 1GB, size=50% for 50% of RAM, or size=512M for 512MB.

Q: What happens when tmpfs runs out of space? A: Applications will receive “No space left on device” errors. Increase size with mount -o remount,size=NEWSIZE or clean up files.

Q: How do I unmount a tmpfs filesystem? A: Use sudo umount /path/to/tmpfs for normal unmount, or sudo umount -f /path/to/tmpfs for forced unmount.

Q: Can I set permissions and ownership for tmpfs? A: Yes, use options like mode=0755 for permissions, uid=1000 for user ownership, and gid=1000 for group ownership.

Q: Is tmpfs data secure? A: tmpfs data can be swapped to disk and is visible in memory dumps. For sensitive data, use encrypted swap and proper cleanup procedures.

Q: What are the best use cases for tmpfs? A: Temporary builds, caching, frequently accessed small files, and any scenario requiring high-speed temporary storage.

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