When you encounter the error -bash: cd: www: Permission denied while trying to navigate into /var/www, it's clearly a permissions issue. Let's break down what's happening based on the ls -l output:

drwxrwxr-- 13 root root  4096 2011-02-26 21:53 www

The directory permissions drwxrwxr-- can be interpreted as:

• d: Directory
• rwx: Owner (root) has read/write/execute
• rwx: Group (root) has read/write/execute
• r--: Others have only read permission

The cd command requires execute (x) permission on a directory. While your user (david) can see the directory contents (r--), the missing execute permission prevents navigation.

Here are the correct ways to resolve this:

1. Change Directory Permissions

sudo chmod o+x /var/www

This adds execute permission for "others". For more security, you might want to:

sudo chmod 755 /var/www

2. Add Your User to the Proper Group

A better approach is to add your user to the web server group (often www-data):

sudo usermod -aG www-data david

Then change group ownership and permissions:

sudo chown -R root:www-data /var/www
sudo chmod -R 775 /var/www

3. Using Sudo Properly

The attempt sudo cd www fails because cd is a shell built-in, not an executable. Instead, use:

sudo -i
cd /var/www

Or more simply:

sudo su
cd /var/www

After making changes, verify with:

ls -ld /var/www

You should see execute permission for your access method (either through group membership or other permissions).

While chmod 777 would "solve" the problem, it's dangerous. Instead:

• Prefer group-based access control
• Maintain proper ownership (root:www-data is common for web directories)
• Consider using ACLs for complex permission scenarios

For more granular control, consider ACLs:

sudo setfacl -Rm u:david:rwx /var/www
sudo setfacl -Rm d:u:david:rwx /var/www

This gives david persistent rwx permissions while maintaining stricter defaults for others.

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When working with Linux systems, directory permissions are crucial for system security and proper functionality. In your case, the /var/www directory has the following permissions:

drwxrwxr-- 13 root root 4096 2011-02-26 21:53 www

Let's break down what this means:

• d: Indicates this is a directory
• rwx: Owner (root) has read, write, and execute permissions
• rwx: Group (root) has read, write, and execute permissions
• r--: Others have only read permission

The cd command requires execute permission on a directory. While your user can read the directory contents (r--), it cannot traverse into it because the execute bit isn't set for "others".

Here are several approaches to resolve this issue:

# Solution 1: Change directory permissions (recommended for development)
sudo chmod o+x /var/www

# Solution 2: Add your user to the www-data group (common for web servers)
sudo usermod -a -G www-data yourusername

# Solution 3: Change directory ownership (use with caution)
sudo chown yourusername:yourusername /var/www -R

You might wonder why sudo cd doesn't work. This is because cd is a shell built-in command, not an external program. When you run:

sudo cd www

The shell tries to find cd in the system PATH before executing built-ins, hence the "command not found" error.

For temporary access without changing permissions:

# Method 1: Use sudo with -i to start a root shell
sudo -i
cd /var/www

# Method 2: Use sudo with bash -c
sudo bash -c "cd /var/www && ls -l"

# Method 3: Create a symbolic link (if you have home directory access)
ln -s /var/www ~/www

For production systems, consider these security recommendations:

# Set secure permissions (user:group as www-data:www-data)
sudo chown -R www-data:www-data /var/www
sudo chmod -R 750 /var/www

# For development environments with multiple users
sudo chown -R :developers /var/www
sudo chmod -R 775 /var/www
sudo setfacl -R -m g:developers:rwx /var/www

If permissions still don't work as expected:

1. Check for SELinux/AppArmor restrictions: ls -Z /var/www
2. Verify parent directory permissions: namei -l /var/www
3. Look for ACLs: getfacl /var/www

Remember that changing system directory permissions can have security implications. Always consider the specific requirements of your environment before implementing these changes.