21.2.2. The vsftpd Server
vsftpd) is designed from the ground up to be fast, stable, and, most importantly, secure.
vsftpdis the only stand-alone
FTPserver distributed with Red Hat Enterprise Linux, due to its ability to handle large numbers of connections efficiently and securely.
vsftpdhas three primary aspects:
- Strong separation of privileged and non-privileged processes — Separate processes handle different tasks, and each of these processes runs with the minimal privileges required for the task.
- Tasks requiring elevated privileges are handled by processes with the minimal privilege necessary — By taking advantage of compatibilities found in the
libcaplibrary, tasks that usually require full root privileges can be executed more safely from a less privileged process.
- Most processes run in a
chrootjail — Whenever possible, processes are change-rooted to the directory being shared; this directory is then considered a
chrootjail. For example, if the
/var/ftp/directory is the primary shared directory,
/var/ftp/to the new root directory, known as
/. This disallows any potential malicious hacker activities for any directories not contained in the new root directory.
vsftpddeals with requests:
- The parent process runs with the least privileges required — The parent process dynamically calculates the level of privileges it requires to minimize the level of risk. Child processes handle direct interaction with the
FTPclients and run with as close to no privileges as possible.
- All operations requiring elevated privileges are handled by a small parent process — Much like the Apache
vsftpdlaunches unprivileged child processes to handle incoming connections. This allows the privileged, parent process to be as small as possible and handle relatively few tasks.
- All requests from unprivileged child processes are distrusted by the parent process — Communication with child processes is received over a socket, and the validity of any information from child processes is checked before being acted on.
- Most interactions with
FTPclients are handled by unprivileged child processes in a
chrootjail — Because these child processes are unprivileged and only have access to the directory being shared, any crashed processes only allow the attacker access to the shared files.
18.104.22.168. Starting and Stopping vsftpd
/etc/rc.d/init.d/vsftpdscript, which can be accessed using the
service vsftpd start
service vsftpd stop
restartoption is a shorthand way of stopping and then starting
vsftpd. This is the most efficient way to make configuration changes take effect after editing the configuration file for
service vsftpd restart
condrestart(conditional restart) option only starts
vsftpdif it is currently running. This option is useful for scripts, because it does not start the daemon if it is not running. The
try-restartoption is a synonym.
service vsftpd condrestart
vsftpdservice does not start automatically at boot time. To configure the
vsftpdservice to start at boot time, use an initscript utility, such as
/sbin/chkconfig, /usr/sbin/ntsysv, or the Services Configuration Tool program. See Chapter 12, Services and Daemons for more information regarding these tools.