NAME

ftpd − The File Transfer Protocol server daemon, including anonymous service

SYNOPSIS

ftpd [−dlxK] [−t timeout] [−T maxtimeout]

OPTIONS

−dDebugging information is sent to the syslogd daemon (see syslogd(8)). 

−lEach FTP session, as well as additional information, such as the file name retrieved or stored, the number of bytes, and the attempted logins that failed, is sent to the syslogd daemon (see syslogd(8)). 

−t time-out
The inactivity time-out period will be set to time-out seconds. 

−T maxtime-out
The maximum timeout period allowed may be set to timeout seconds with this option. 

−xEncrypts the data transmitted between the local host and the remote host. This option requires that the local and remote hosts be configured to use Kerberos authentication in the same or trusting Kerberos realms. 

If the ftpd daemon is started with the −x option, only connections initiated with the −x option from a remote host will be accepted.  All communications between the two hosts will be encrypted. 

−KSpecifies that only Kerberos authenticated connections will be accepted. This option requires that the local and remote hosts be configured to use Kerberos authentication in the same or trusting Kerberos realms. 

If the ftpd daemon is started with the −K option, only connections initiated from a host in the same or trusting Kerberos domain will be accepted. All communications between the two hosts will be encrypted. 

SECURITY NOTE

This security-sensitive command uses the SIA (Security Integration Architecture) routine as an interface to the security mechanisms. See matrix.conf(4) for more information. 

DESCRIPTION

The ftpd command is the DARPA (Defense Advanced Research Projects Agency) Internet File Transfer Protocol server process.  The server uses the TCP protocol and listens at the port specified in the FTP service specification; see services(4). 

The FTP server will time out an inactive session after 15 minutes. If the −t option is specified, the inactivity time-out period will be set to time-out seconds. A client may also request a different time-out period; the maximum period allowed may be set to time-out seconds with the −T option. The default limit is 2 hours. 

If you want to use a customized banner, create an /etc/banner file. The ftpd daemon reads the file, if it exists, and writes its contents over a new FTP connection prior to starting the login dialog. 

The ftpd command interprets file names according to the “globbing” conventions used by the C shell (see csh(1)). This interpretation allows users to utilize the metacharacters “∗?[]{}~”. 

The way in which the ftpd daemon authenticates a user and transmits data depends on if the local and remote hosts are using a basic connection or a secure connection (Kerberos). Basic and secure connections provide user authentication; however, a secure connection also provides client and server authentication, data encryption, data integrity, and nonrepudiation. 

Basic Connection

A basic connection is one where the ftpd daemon authenticates users according to four rules:

       •The username must be in the password database, /etc/passwd, and not have a null password.  In this case, a password must be provided by the client before any file operations may be performed. 

       •The username must not appear in the /etc/ftpusers file. 

       •The user must have a standard shell returned by the getusershell() call (see getusershell(3)). 

       •If the username is anonymous or ftp, an anonymous ftp account must be present in the /etc/passwd file (user ftp).  In this case, the user is allowed to log in by specifying any password (by convention this is given as the client host’s name). 

Secure Connection

A secure connection is one where the ftpd daemon authenticates a user by using Kerberos. Kerberos is a client/server application that authenticate the client, server, and user, encrypt data, and ensure data integrity and nonrepudiation.  See your system administrator to determine if your system is running Kerberos. See Security Administration for more information about Kerberos. 

Kerberos authenticates by using secret-key cryptography and tickets between Kerberos clients and Kerberos server in the same or trusting Kerberos realms. Once authenticated by Kerberos, users receive a Kerberos Ticket Granting Ticket (TGT). Users with a valid TGT are not prompted for a username or password when the remote host is in the same or trusting Kerberos realm. 

FTP REQUESTS

The FTP server currently supports the following ftp requests; case is not distinguished:

The following nonstandard or UNIX compatible commands are supported by the SITE request:

The remaining ftp requests specified in Internet RFC 959 are recognized, but not implemented.  MDTM and SIZE are not specified in RFC 959, but will appear in the next updated FTP RFC. 

TYPE-OF-SERVICE VALUES

The ftp command uses the default Type-of-Service values recommended by RFC1060, which are as follows:

ftp-control
Low delay

ftp-data
High throughput

Anonymous FTP Configuration

If you are creating an anonymous FTP account, ftpd takes special measures to restrict the client’s access privileges when the user logs in.  The server executes a chroot call (see chroot(2)) to the home directory of the ftp user. In order that system security is not breached, it is recommended that you adhere to the following rules when creating directories and files in the ftp subtree:

~ftp
Make the home directory owned by the superuser (root) and unwritable by anyone.

~ftp/bin
Make this directory owned by the superuser and unwritable by anyone.  The ls program (see ls(1)) must be present to support the list command. This program should have mode 111. 

Copy the ls program from /sbin/ls.  This is the statically linked version of the ls command, which does not require shared library support.  Be sure to copy the static version of ls from the /sbin directory, not the shared version from the /usr/bin directory. 

~ftp/etc
Make this directory owned by the superuser and unwritable by anyone.  The passwd and group files (see passwd(4) and group(4) ) must be present for the ls command to be able to produce owner names rather than numbers. The password field in the passwd file is not used, and should not contain real encrypted passwords.  These files should be mode 444. 

In this environment, the sia subdirectory (which you can copy from /etc/sia) must also be present for the ls command to be able to produce owner names rather than numbers. 

~ftp/pub
Make this directory mode 777 and owned by ftp.  Users should then place files that are to be accessible via the anonymous account in this directory. 

You can configure these values by specifying them in the /etc/iptos file. For more information, see iptos(4). 

FILES

/usr/sbin/ftpd
Specifies the command path.

/etc/ftpusers
Contains the list of unauthorized users.

/etc/banner
Specifies the path name for the banner file.

CAUTIONS

The anonymous account is inherently dangerous and should be avoided when possible. 

The server must run as the superuser to create sockets with privileged port numbers.  It maintains an effective user ID of the logged in user, reverting to the superuser only when binding addresses to sockets.  The possible security holes have been extensively scrutinized, but are possibly incomplete. 

SEE ALSO

Commands: ftp(1), syslogd(8)

Functions: getusershell(3)

Files: iptos(4)

Guides: Security Administration