如何借助fswatch与xargs自动修改/var/www/html的权限及属主？

Hey there! Let's get this auto-permission setup working for your /var/www/html directory. Here's how to do it properly, with some optimizations to avoid common pitfalls:

Basic Implementation #

If you want a quick-and-dirty solution that refreshes permissions across the entire directory whenever any change happens, use this command:

fswatch -o /var/www/html | xargs -I {} sh -c 'chown -R www-data:www-data /var/www/html && chmod -R 755 /var/www/html'

Breakdown: #

• -o tells fswatch to output a single newline per batch of events (instead of every individual event), which prevents spamming the chown/chmod commands for a single file creation.
• xargs -I {} replaces the placeholder with the trigger from fswatch, then runs the shell command to fix ownership and permissions.
• chown -R recursively sets the owner/group to www-data (adjust this to match your web server's user/group, e.g., apache for Apache).
• chmod -R 755 sets read/execute permissions for everyone and full access for the owner (good for directories, but files can be more restrictive).

Optimized Version (Target Only Changed Files) #

Recursively modifying the entire directory every time a single file changes is inefficient, and can trigger infinite loops (since chown/chmod themselves modify file attributes, which fswatch detects). Instead, target only the changed files/directories:

fswatch -x /var/www/html | grep -E "(Created|Updated)" | awk '{print $NF}' | xargs -I {} sh -c '
    chown www-data:www-data {}
    if [ -d {} ]; then
        chmod 755 {}
    else
        chmod 644 {}
    fi
'

Breakdown: #

• -x makes fswatch output the event type (e.g., Created, Updated) alongside the file path.
• grep -E "(Created|Updated)" filters out irrelevant events like permission changes or deletions (we don't need to fix permissions for deleted files!).
• awk '{print $NF}' extracts just the file/directory path from the output.
• The shell command checks if the path is a directory or file, then applies appropriate permissions: 755 for directories (so users can traverse them) and 644 for files (read-only for everyone except the owner).

Run in the Background (Systemd Service) #

To make this watcher run automatically on boot and stay in the background, create a systemd service file:

1. Create the service file:

sudo nano /etc/systemd/system/www-perms-watcher.service

2. Paste this content (adjust user/group and paths if needed):

[Unit]
Description=Watch /var/www/html for changes and auto-fix permissions
After=network.target

[Service]
User=root
ExecStart=/usr/bin/fswatch -x /var/www/html | /usr/bin/grep -E "(Created|Updated)" | /usr/bin/awk '{print $NF}' | /usr/bin/xargs -I {} /bin/sh -c 'chown www-data:www-data {} && if [ -d {} ]; then chmod 755 {}; else chmod 644 {}; fi'
Restart=always

[Install]
WantedBy=multi-user.target

3. Enable and start the service:

sudo systemctl daemon-reload
sudo systemctl enable --now www-perms-watcher.service

Key Notes #

• Adjust User/Group: Replace www-data with your web server's actual user (e.g., apache for Apache, nginx for some Nginx setups).
• Permission Values: Tweak 755/644 if your use case requires more permissive settings (e.g., 775 for directories that need group write access), but prioritize security where possible.
• Test First: Run the fswatch command in your terminal first to verify it works before setting up the systemd service. This helps catch any path or permission issues upfront.

内容的提问来源于stack exchange，提问作者Tejas Shah