Chattr in action

 # lsattr /var/log/messages
 -------------- /var/log/messages

 # chattr +a /var/log/messages
 # lsattr /var/log/messages
 ---a---------- /var/log/messages

 # echo "Please truncate file" > /var/log/messages
 Operation not permitted

 # echo "Please append to file" >> /var/log/messages
 (no error)

 # chattr -a /var/log/messages
 # chattr +i /var/log/messages
 # lsattr /var/log/messages
 ---i---------- /var/log/messages

 # echo "Please append to file" >> /var/log/messages
 Permission denied