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File and Print Servers

This chapter guides you through the installation and configuration of Samba, an open source implementation of the Server Message Block (SMB) and common Internet file system (CIFS) protocol, and vsftpd, the primary FTP server shipped with Fedora. Additionally, it explains how to use the Printer tool to configure printers.

Samba

Documentation for configuring and using Samba has been removed due to being outdated. Use Red Hat Enterprise Linux 9 Samba documentation instead.

FTP

File Transfer Protocol (FTP) is one of the oldest and most commonly used protocols found on the Internet today. Its purpose is to reliably transfer files between computer hosts on a network without requiring the user to log directly into the remote host or have knowledge of how to use the remote system. It allows users to access files on remote systems using a standard set of simple commands.

This section outlines the basics of the FTP protocol, as well as configuration options for the primary FTP server shipped with Fedora, vsftpd.

The File Transfer Protocol

However, because FTP is so prevalent on the Internet, it is often required to share files to the public. System administrators, therefore, should be aware of the FTP protocol’s unique characteristics.

Multiple Ports, Multiple Modes

Unlike most protocols used on the Internet, FTP requires multiple network ports to work properly. When an FTP client application initiates a connection to an FTP server, it opens port 21 on the server — known as the command port. This port is used to issue all commands to the server. Any data requested from the server is returned to the client via a data port. The port number for data connections, and the way in which data connections are initialized, vary depending upon whether the client requests the data in active or passive mode.

The following defines these modes:

active mode: Active mode is the original method used by the FTP protocol for transferring data to the client application. When an active mode data transfer is initiated by the FTP client, the server opens a connection from port 20 on the server to the IP address and a random, unprivileged port (greater than 1024) specified by the client. This arrangement means that the client machine must be allowed to accept connections over any port above 1024. With the growth of insecure networks, such as the Internet, the use of firewalls to protect client machines is now prevalent. Because these client-side firewalls often deny incoming connections from active mode FTP servers, passive mode was devised.
passive mode: Passive mode, like active mode, is initiated by the FTP client application. When requesting data from the server, the FTP client indicates it wants to access the data in passive mode and the server provides the IP address and a random, unprivileged port (greater than 1024) on the server. The client then connects to that port on the server to download the requested information.

While passive mode resolves issues for client-side firewall interference with data connections, it can complicate administration of the server-side firewall. You can reduce the number of open ports on a server by limiting the range of unprivileged ports on the FTP server. This also simplifies the process of configuring firewall rules for the server. See Network Options for more information about limiting passive ports.

FTP Servers

Fedora ships with two different FTP servers:

proftpd - A fast, stable, and highly configurable FTP server.
vsftpd — A fast, secure FTP daemon which is the preferred FTP server for Fedora. The remainder of this section focuses on vsftpd.

vsftpd

The Very Secure FTP Daemon (vsftpd) is designed from the ground up to be fast, stable, and, most importantly, secure. vsftpd is the only stand-alone FTP server distributed with Fedora, due to its ability to handle large numbers of connections efficiently and securely.

The security model used by vsftpd has three primary aspects:

Strong separation of privileged and non-privileged processes — Separate processes handle different tasks, and each of these processes run with the minimal privileges required for the task.
Tasks requiring elevated privileges are handled by processes with the minimal privilege necessary — By leveraging compatibilities found in the libcap library, tasks that usually require full root privileges can be executed more safely from a less privileged process.
Most processes run in a chroot jail — Whenever possible, processes are change-rooted to the directory being shared; this directory is then considered a chroot jail. For example, if the directory /var/ftp/ is the primary shared directory, vsftpd reassigns /var/ftp/ to the new root directory, known as /. This disallows any potential malicious hacker activities for any directories not contained below the new root directory.

Use of these security practices has the following effect on how vsftpd deals 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 FTP clients 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 HTTP Server, vsftpd launches 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 are received over a socket, and the validity of any information from child processes is checked before being acted on.
Most interaction with FTP clients is handled by unprivileged child processes in a chroot jail — Because these child processes are unprivileged and only have access to the directory being shared, any crashed processes only allows the attacker access to the shared files.

Files Installed with vsftpd

The vsftpd RPM installs the daemon (/usr/sbin/vsftpd), its configuration and related files, as well as FTP directories onto the system. The following lists the files and directories related to vsftpd configuration:

/etc/rc.d/init.d/vsftpd — The initialization script (initscript) used by the systemctl command to start, stop, or reload vsftpd. See Starting and Stopping vsftpd for more information about using this script.
/etc/pam.d/vsftpd — The Pluggable Authentication Modules (PAM) configuration file for vsftpd. This file specifies the requirements a user must meet to login to the FTP server. For more information on PAM, refer to the Using Pluggable Authentication Modules (PAM) chapter of the Fedora 38 Managing Single Sign-On and Smart Cards guide.
/etc/vsftpd/vsftpd.conf — The configuration file for vsftpd. See vsftpd Configuration Options for a list of important options contained within this file.
/etc/vsftpd/ftpusers — A list of users not allowed to log into vsftpd. By default, this list includes the root, bin, and daemon users, among others.
/etc/vsftpd/user_list — This file can be configured to either deny or allow access to the users listed, depending on whether the userlist_deny directive is set to YES (default) or NO in /etc/vsftpd/vsftpd.conf. If /etc/vsftpd/user_list is used to grant access to users, the usernames listed must not appear in /etc/vsftpd/ftpusers.
/var/ftp/ — The directory containing files served by vsftpd. It also contains the /var/ftp/pub/ directory for anonymous users. Both directories are world-readable, but writable only by the root user.

Starting and Stopping vsftpd

The vsftpd RPM installs the /etc/rc.d/init.d/vsftpd script, which can be accessed using the systemctl command.

To start the server, as root type:

systemctl start vsftpd.service

To stop the server, as root type:

systemctl stop vsftpd.service

The restart option 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 vsftpd.

To restart the server, as root type:

systemctl restart vsftpd.service

The condrestart (conditional restart) option only starts vsftpd if it is currently running. This option is useful for scripts, because it does not start the daemon if it is not running.

To conditionally restart the server, as root type:

systemctl condrestart vsftpd.service

By default, the vsftpd service does not start automatically at boot time. To configure the vsftpd service to start at boot time, use a service manager such as systemctl. See Services and Daemons for more information on how to configure services in Fedora.

Configuring the Firewall for FTP

By default, firewalld blocks incoming FTP connections. To allow FTP connections, as root type:

firewall-cmd --add-service=ftp

The change will be applied immediately, but will be lost next time firewalld is reloaded or the system restarted. To make it permanent, type:

firewall-cmd --permanent --add-service=ftp

For more information on configuring firewalld, see the Red Hat Enterprise Linux 7 Security Guide.

Starting Multiple Copies of vsftpd

Sometimes one computer is used to serve multiple FTP domains. This is a technique called multihoming. One way to multihome using vsftpd is by running multiple copies of the daemon, each with its own configuration file.

To do this, first assign all relevant IP addresses to network devices or alias network devices on the system. For more information about configuring network devices, device aliases, and additional information about network configuration scripts, refer to the Fedora Networking Guide.

Next, the DNS server for the FTP domains must be configured to reference the correct machine. For information about BIND and its configuration files, refer to the Fedora Networking Guide.

If there is more configuration files present in the /etc/vsftpd directory, calling systemctl start vsftpd.service results in the /etc/rc.d/init.d/vsftpd initscript starting the same number of processes as the number of configuration files. Each configuration file must have a unique name in the /etc/vsftpd/ directory and must be readable and writable only by root.

vsftpd Configuration Options

Although vsftpd may not offer the level of customization other widely available FTP servers have, it offers enough options to fill most administrator’s needs. The fact that it is not overly feature-laden limits configuration and programmatic errors.

All configuration of vsftpd is handled by its configuration file, /etc/vsftpd/vsftpd.conf. Each directive is on its own line within the file and follows the following format:

directive=value

For each directive, replace directive with a valid directive and value with a valid value.

Do not use spaces

There must not be any spaces between the directive, equal symbol, and the value in a directive.

Comment lines must be preceded by a hash sign (#) and are ignored by the daemon.

For a complete list of all directives available, refer to the man page for vsftpd.conf.

Securing the vsftpd service

For an overview of ways to secure vsftpd, see the Red Hat Enterprise Linux 7 Security Guide.

The following is a list of some of the more important directives within /etc/vsftpd/vsftpd.conf. All directives not explicitly found or commented out within vsftpd's configuration file are set to their default value.

Daemon Options

The following is a list of directives which control the overall behavior of the vsftpd daemon.

listen — When enabled, vsftpd runs in stand-alone mode. Fedora sets this value to YES. This directive cannot be used in conjunction with the listen_ipv6 directive.

The default value is NO.
listen_ipv6 — When enabled, vsftpd runs in stand-alone mode, but listens only to IPv6 sockets. This directive cannot be used in conjunction with the listen directive.

The default value is NO.
session_support — When enabled, vsftpd attempts to maintain login sessions for each user through Pluggable Authentication Modules (PAM). For more information, refer to the Using Pluggable Authentication Modules (PAM) chapter of the Red Hat Enterprise Linux 6 Managing Single Sign-On and Smart Cards and the PAM man pages. . If session logging is not necessary, disabling this option allows vsftpd to run with less processes and lower privileges.

The default value is YES.

The following is a list of directives which control the login behavior and access control mechanisms.

anonymous_enable — When enabled, anonymous users are allowed to log in. The usernames anonymous and ftp are accepted.

The default value is YES.

See Anonymous User Options for a list of directives affecting anonymous users.
banned_email_file — If the deny_email_enable directive is set to YES, this directive specifies the file containing a list of anonymous email passwords which are not permitted access to the server.

The default value is /etc/vsftpd/banned_emails.
banner_file — Specifies the file containing text displayed when a connection is established to the server. This option overrides any text specified in the ftpd_banner directive.

There is no default value for this directive.
cmds_allowed — Specifies a comma-delimited list of FTP commands allowed by the server. All other commands are rejected.

There is no default value for this directive.
deny_email_enable — When enabled, any anonymous user utilizing email passwords specified in the /etc/vsftpd/banned_emails are denied access to the server. The name of the file referenced by this directive can be specified using the banned_email_file directive.

The default value is NO.
ftpd_banner — When enabled, the string specified within this directive is displayed when a connection is established to the server. This option can be overridden by the banner_file directive.

By default vsftpd displays its standard banner.
local_enable — When enabled, local users are allowed to log into the system.

The default value is YES.

See Local User Options for a list of directives affecting local users.
pam_service_name — Specifies the PAM service name for vsftpd.

The default value is ftp. Note, in Fedora, the value is set to vsftpd.
The default value is NO. Note, in Fedora, the value is set to YES.
userlist_deny — When used in conjunction with the userlist_enable directive and set to NO, all local users are denied access unless the username is listed in the file specified by the userlist_file directive. Because access is denied before the client is asked for a password, setting this directive to NO prevents local users from submitting unencrypted passwords over the network.

The default value is YES.
userlist_enable — When enabled, the users listed in the file specified by the userlist_file directive are denied access. Because access is denied before the client is asked for a password, users are prevented from submitting unencrypted passwords over the network.

The default value is NO, however under Fedora the value is set to YES.
userlist_file — Specifies the file referenced by vsftpd when the userlist_enable directive is enabled.

The default value is /etc/vsftpd/user_list and is created during installation.

Anonymous User Options

The following lists directives which control anonymous user access to the server. To use these options, the anonymous_enable directive must be set to YES.

anon_mkdir_write_enable — When enabled in conjunction with the write_enable directive, anonymous users are allowed to create new directories within a parent directory which has write permissions.

The default value is NO.
anon_root — Specifies the directory vsftpd changes to after an anonymous user logs in.

There is no default value for this directive.
anon_upload_enable — When enabled in conjunction with the write_enable directive, anonymous users are allowed to upload files within a parent directory which has write permissions.

The default value is NO.
anon_world_readable_only — When enabled, anonymous users are only allowed to download world-readable files.

The default value is YES.
ftp_username — Specifies the local user account (listed in /etc/passwd) used for the anonymous FTP user. The home directory specified in /etc/passwd for the user is the root directory of the anonymous FTP user.

The default value is ftp.
no_anon_password — When enabled, the anonymous user is not asked for a password.

The default value is NO.
secure_email_list_enable — When enabled, only a specified list of email passwords for anonymous logins are accepted. This is a convenient way to offer limited security to public content without the need for virtual users.

Anonymous logins are prevented unless the password provided is listed in /etc/vsftpd/email_passwords. The file format is one password per line, with no trailing white spaces.

The default value is NO.

Local User Options

The following lists directives which characterize the way local users access the server. To use these options, the local_enable directive must be set to YES.

chmod_enable — When enabled, the FTP command SITE CHMOD is allowed for local users. This command allows the users to change the permissions on files.

The default value is YES.
chroot_list_enable — When enabled, the local users listed in the file specified in the chroot_list_file directive are placed in a chroot jail upon log in.

If enabled in conjunction with the chroot_local_user directive, the local users listed in the file specified in the chroot_list_file directive are not placed in a chroot jail upon log in.

The default value is NO.
chroot_list_file — Specifies the file containing a list of local users referenced when the chroot_list_enable directive is set to YES.

The default value is /etc/vsftpd/chroot_list.

chroot_local_user — When enabled, local users are change-rooted to their home directories after logging in.

The default value is NO.

Avoid enabling the chroot_local_user option

Enabling chroot_local_user opens up a number of security issues, especially for users with upload privileges. For this reason, it is not recommended.

guest_enable — When enabled, all non-anonymous users are logged in as the user guest, which is the local user specified in the guest_username directive.

The default value is NO.
guest_username — Specifies the username the guest user is mapped to.

The default value is ftp.
local_root — Specifies the directory vsftpd changes to after a local user logs in.

There is no default value for this directive.
local_umask — Specifies the umask value for file creation. Note that the default value is in octal form (a numerical system with a base of eight), which includes a “0” prefix. Otherwise the value is treated as a base-10 integer.

The default value is 022.
passwd_chroot_enable — When enabled in conjunction with the chroot_local_user directive, vsftpd change-roots local users based on the occurrence of the /./ in the home directory field within /etc/passwd.

The default value is NO.
user_config_dir — Specifies the path to a directory containing configuration files bearing the name of local system users that contain specific setting for that user. Any directive in the user’s configuration file overrides those found in /etc/vsftpd/vsftpd.conf.

There is no default value for this directive.

Directory Options

The following lists directives which affect directories.

dirlist_enable — When enabled, users are allowed to view directory lists.

The default value is YES.
dirmessage_enable — When enabled, a message is displayed whenever a user enters a directory with a message file. This message resides within the current directory. The name of this file is specified in the message_file directive and is .message by default.

The default value is NO. Note, in Fedora, the value is set to YES.
force_dot_files — When enabled, files beginning with a dot (.) are listed in directory listings, with the exception of the . and .. files.

The default value is NO.
hide_ids — When enabled, all directory listings show ftp as the user and group for each file.

The default value is NO.
message_file — Specifies the name of the message file when using the dirmessage_enable directive.

The default value is .message.
text_userdb_names — When enabled, text usernames and group names are used in place of UID and GID entries. Enabling this option may slow performance of the server.

The default value is NO.
use_localtime — When enabled, directory listings reveal the local time for the computer instead of GMT.

The default value is NO.

File Transfer Options

The following lists directives which affect directories.

download_enable — When enabled, file downloads are permitted.

The default value is YES.
chown_uploads — When enabled, all files uploaded by anonymous users are owned by the user specified in the chown_username directive.

The default value is NO.
chown_username — Specifies the ownership of anonymously uploaded files if the chown_uploads directive is enabled.

The default value is root.
write_enable — When enabled, FTP commands which can change the file system are allowed, such as DELE, RNFR, and STOR.

The default value is YES.

Logging Options

The following lists directives which affect vsftpd's logging behavior.

dual_log_enable — When enabled in conjunction with xferlog_enable, vsftpd writes two files simultaneously: a wu-ftpd-compatible log to the file specified in the xferlog_file directive (/var/log/xferlog by default) and a standard vsftpd log file specified in the vsftpd_log_file directive (/var/log/vsftpd.log by default).

The default value is NO.
log_ftp_protocol — When enabled in conjunction with xferlog_enable and with xferlog_std_format set to NO, all FTP commands and responses are logged. This directive is useful for debugging.

The default value is NO.
syslog_enable — When enabled in conjunction with xferlog_enable, all logging normally written to the standard vsftpd log file specified in the vsftpd_log_file directive (/var/log/vsftpd.log by default) is sent to the system logger instead under the FTPD facility.

The default value is NO.
vsftpd_log_file — Specifies the vsftpd log file. For this file to be used, xferlog_enable must be enabled and xferlog_std_format must either be set to NO or, if xferlog_std_format is set to YES, dual_log_enable must be enabled. It is important to note that if syslog_enable is set to YES, the system log is used instead of the file specified in this directive.

The default value is /var/log/vsftpd.log.
xferlog_enable — When enabled, vsftpd logs connections (vsftpd format only) and file transfer information to the log file specified in the vsftpd_log_file directive (/var/log/vsftpd.log by default). If xferlog_std_format is set to YES, file transfer information is logged but connections are not, and the log file specified in xferlog_file (/var/log/xferlog by default) is used instead. It is important to note that both log files and log formats are used if dual_log_enable is set to YES.

The default value is NO. Note, in Fedora, the value is set to YES.
xferlog_file — Specifies the wu-ftpd-compatible log file. For this file to be used, xferlog_enable must be enabled and xferlog_std_format must be set to YES. It is also used if dual_log_enable is set to YES.

The default value is /var/log/xferlog.
xferlog_std_format — When enabled in conjunction with xferlog_enable, only a wu-ftpd-compatible file transfer log is written to the file specified in the xferlog_file directive (/var/log/xferlog by default). It is important to note that this file only logs file transfers and does not log connections to the server.

The default value is NO. Note, in Fedora, the value is set to YES.

Maintaining compatibility with older log file formats

To maintain compatibility with log files written by the older wu-ftpd FTP server, the xferlog_std_format directive is set to YES under Fedora. However, this setting means that connections to the server are not logged.

To both log connections in vsftpd format and maintain a wu-ftpd-compatible file transfer log, set dual_log_enable to YES.

If maintaining a wu-ftpd-compatible file transfer log is not important, either set xferlog_std_format to NO, comment the line with a hash sign (#), or delete the line entirely.

Network Options

The following lists directives which affect how vsftpd interacts with the network.

accept_timeout — Specifies the amount of time for a client using passive mode to establish a connection.

The default value is 60.
anon_max_rate — Specifies the maximum data transfer rate for anonymous users in bytes per second.

The default value is 0, which does not limit the transfer rate.
connect_from_port_20 When enabled, vsftpd runs with enough privileges to open port 20 on the server during active mode data transfers. Disabling this option allows vsftpd to run with less privileges, but may be incompatible with some FTP clients.

The default value is NO. Note, in Fedora, the value is set to YES.
connect_timeout — Specifies the maximum amount of time a client using active mode has to respond to a data connection, in seconds.

The default value is 60.
data_connection_timeout — Specifies maximum amount of time data transfers are allowed to stall, in seconds. Once triggered, the connection to the remote client is closed.

The default value is 300.
ftp_data_port — Specifies the port used for active data connections when connect_from_port_20 is set to YES.

The default value is 20.
idle_session_timeout — Specifies the maximum amount of time between commands from a remote client. Once triggered, the connection to the remote client is closed.

The default value is 300.

listen_address — Specifies the IP address on which vsftpd listens for network connections.

There is no default value for this directive.

Running multiple copies of vsftpd

If running multiple copies of vsftpd serving different IP addresses, the configuration file for each copy of the vsftpd daemon must have a different value for this directive. See Starting Multiple Copies of vsftpd for more information about multihomed FTP servers.

listen_address6 — Specifies the IPv6 address on which vsftpd listens for network connections when listen_ipv6 is set to YES.