After accidentally copying files to a USB drive with overly permissive 777 settings, we need to restore proper permissions in the user's home directory. This means:

• Directories should be 775 (drwxrwxr-x)
• Regular files should be 664 (-rw-rw-r--)
• No files need execute permissions (as they're documents/media)

Here's the most efficient one-liner using find:

find /home/username -type d -exec chmod 775 {} \;
find /home/username -type f -exec chmod 664 {} \;

For better error handling and logging:

#!/bin/bash

TARGET_DIR="/home/username"
LOG_FILE="/var/log/permission_fix.log"

echo "Starting permission correction at $(date)" > $LOG_FILE

# Fix directory permissions
find "$TARGET_DIR" -type d -print0 | while IFS= read -r -d '' dir; do
    if [[ "$dir" != "$TARGET_DIR" ]]; then
        chmod -v 775 "$dir" >> $LOG_FILE 2>&1
    fi
done

# Fix file permissions
find "$TARGET_DIR" -type f -print0 | while IFS= read -r -d '' file; do
    chmod -v 664 "$file" >> $LOG_FILE 2>&1
done

echo "Permission correction completed at $(date)" >> $LOG_FILE

For environments with ACLs or special requirements:

# Preserve original ownership while fixing permissions
find /home/username -exec chmod --reference=/etc/skel {} \;

# Alternative with getfacl/setfacl
getfacl -R /home/username > permissions_backup.acl
# After permission changes...
setfacl --restore=permissions_backup.acl

Check your work with these commands:

# Find directories with wrong permissions
find /home/username -type d ! -perm 775 -ls

# Find files with wrong permissions
find /home/username -type f ! -perm 664 -ls

# Count affected items
find /home/username -type d ! -perm 775 | wc -l
find /home/username -type f ! -perm 664 | wc -l

Recently encountered a common headache when migrating data - a whole directory tree copied with 777 permissions. This creates security risks, especially when dealing with user home directories where:

• Directories require execute (x) for traversal
• Regular files (images/docs/MP3s) should never be executable
• Group permissions should allow shared access where needed

This atomic command handles both directory and file permission correction:

find /home/user/target_dir -type d -exec chmod 775 {} + -o -type f -exec chmod 664 {} +

Breakdown:

• -type d: Processes directories first with 775 (rwxrwxr-x)
• -o: Logical OR for the file processing branch
• -type f: Applies 664 (rw-rw-r--) to regular files
• -exec {} +: Batch processing for efficiency

For systems using ACLs or special bits (setuid/sticky), add these safeguards:

# Preserve existing special permission bits
find /path -type d -exec chmod u=rwx,g=rwx,o=rx {} +
find /path -type f -exec chmod u=rw,g=rw,o=r {} +

After bulk changes, verify with this audit script:

#!/bin/bash
TARGET_DIR="/home/user/files"

echo "Checking directory permissions:"
find "$TARGET_DIR" -type d ! -perm 775 -ls

echo -e "\nChecking file permissions:"
find "$TARGET_DIR" -type f ! -perm 664 -ls

For future transfers, use rsync's permission control:

rsync -av --chmod=D775,F664 source/ user@host:destination/

Key flags:

• D775: Directory permissions
• F664: File permissions
• --no-perms: Optional to ignore source permissions

Add these to your ~/.bashrc for safe copying:

alias cp='cp --no-preserve=mode'
alias scp='scp -p'  # Preserves original permissions