Internet File Transfer Protocol server

is the Internet File Transfer Protocol server process. The server uses the TCP protocol and listens at the port specified in the service specification; see services(5) .

Available options:

-a anondir

Define anondir as the directory to chroot() into for anonymous logins. Default is the home directory for the ftp user. This can also be specified with the ftpd.conf() directive.

-c confdir

Change the root directory of the configuration files from to confdir . This changes the directory for the following files: /etc/ftpchroot , /etc/ftpusers , /etc/ftpwelcome , /etc/motd , and the file specified by the ftpd.conf() directive.

-C user

Check whether user would be granted access under the restrictions given in ftpusers() and exit without attempting a connection. exits with an exit code of 0 if access would be granted, or 1 otherwise. This can be useful for testing configurations.

-d

Debugging information is written to the syslog using a facility of LOG_FTP .

-e emailaddr

Use emailaddr for the escape sequence (see

-h hostname

Explicitly set the hostname to advertise as to hostname . The default is the hostname associated with the IP address that is listening on. This ability (with or without -h ) , in conjunction with -c confdir , is useful when configuring FTP servers, each listening on separate addresses as separate names. Refer to inetd.conf() for more information on starting services to listen on specific IP addresses.

-H

Equivalent to -h `hostname`

-l

Each successful and failed FTP session is logged using syslog with a facility of LOG_FTP . If this option is specified more than once, the retrieve (get), store (put), append, delete, make directory, remove directory and rename operations and their file name arguments are also logged.

-P dataport

Use dataport as the data port, overriding the default of using the port one less that the port is listening on.

-q

Enable the use of pid files for keeping track of the number of logged-in users per class. This is the default.

-Q

Disable the use of pid files for keeping track of the number of logged-in users per class. This may reduce the load on heavily loaded FTP servers.

-r

Permanently drop root privileges once the user is logged in. The use of this option may result in the server using a port other than the (listening-port - 1) for style commands, which is contrary to the RFC 959 specification, but in practice very few clients rely upon this behaviour. See below for more details.

-s

Require a secure authentication mechanism like Kerberos or S/Key to be used.

-u

Log each concurrent FTP session to /var/run/utmp , making them visible to commands such as who(1) .

-U

Don't log each concurrent FTP session to /var/run/utmp . This is the default.

-V version

Use version as the version to advertise in the login banner and in the output of and instead of the default version information. If version is empty or then don't display any version information.

-w

Log each FTP session to /var/log/wtmp , making them visible to commands such as last(1) . This is the default.

-W

Don't log each FTP session to /var/log/wtmp .

-X

Log WU-FTPD style entries to the syslog, prefixed with using a facility of LOG_FTP . These syslog entries can be converted to a WU-FTPD style xferlog file suitable for input into a third-party log analysis tool with a command similar to:

The file /etc/nologin can be used to disable FTP access. If the file exists, displays it and exits. If the file /etc/ftpwelcome exists, prints it before issuing the message. If the file /etc/motd exists (under the chroot directory if applicable), prints it after a successful login. This may be changed with the ftpd.conf() directive

The server currently supports the following FTP requests. The case of the requests is ignored.

Sy Request Ta Sy Description

ABOR Ta abort previous command

ACCT Ta specify account (ignored)

ALLO Ta allocate storage (vacuously)

APPE Ta append to a file

CDUP Ta change to parent of current working directory

CWD Ta change working directory

DELE Ta delete a file

EPSV Ta prepare for server-to-server transfer

EPRT Ta specify data connection port

FEAT Ta list extra features that are not defined in RFC 959

HELP Ta give help information

LIST Ta give list files in a directory Pq Dq ls -lA

LPSV Ta prepare for server-to-server transfer

LPRT Ta specify data connection port

MLSD Ta list contents of directory in a machine-processable form

MLST Ta show a pathname in a machine-processable form

MKD Ta make a directory

MDTM Ta show last modification time of file

MODE Ta specify data transfer Em mode

NLST Ta give name list of files in directory

NOOP Ta do nothing

OPTS Ta define persistent options for a given command

PASS Ta specify password

PASV Ta prepare for server-to-server transfer

PORT Ta specify data connection port

PWD Ta print the current working directory

QUIT Ta terminate session

REST Ta restart incomplete transfer

RETR Ta retrieve a file

RMD Ta remove a directory

RNFR Ta specify rename-from file name

RNTO Ta specify rename-to file name

SITE Ta non-standard commands (see next section)

SIZE Ta return size of file

STAT Ta return status of server

STOR Ta store a file

STOU Ta store a file with a unique name

STRU Ta specify data transfer Em structure

SYST Ta show operating system type of server system

TYPE Ta specify data transfer Em type

USER Ta specify user name

XCUP Ta change to parent of current working directory (deprecated)

XCWD Ta change working directory (deprecated)

XMKD Ta make a directory (deprecated)

XPWD Ta print the current working directory (deprecated)

XRMD Ta remove a directory (deprecated)

The following non-standard or specific commands are supported by the SITE request.

Sy Request Ta Sy Description

CHMOD Ta change mode of a file, e.g. ``SITE CHMOD 755 filename''

HELP Ta give help information.

IDLE Ta set idle-timer, e.g. ``SITE IDLE 60''

RATEGET Ta set maximum get rate throttle in bytes/second, e.g. ``SITE RATEGET 5k''

RATEPUT Ta set maximum put rate throttle in bytes/second, e.g. ``SITE RATEPUT 5k''

UMASK Ta change umask, e.g. ``SITE UMASK 002''

The following FTP requests (as specified in RFC 959 ) are recognized, but are not implemented: and and are not specified in RFC 959 , but will appear in the next updated FTP RFC.

The server will abort an active file transfer only when the command is preceded by a Telnet "Interrupt Process" (IP) signal and a Telnet "Synch" signal in the command Telnet stream, as described in Internet RFC 959 . If a command is received during a data transfer, preceded by a Telnet IP and Synch, transfer status will be returned.

interprets file names according to the conventions used by csh(1) . This allows users to utilize the metacharacters

authenticates users according to five rules.

•

The login name must be in the password data base, /etc/pwd.db , and not have a null password. In this case a password must be provided by the client before any file operations may be performed. If the user has an S/Key key, the response from a successful command will include an S/Key challenge. The client may choose to respond with a command giving either a standard password or an S/Key one-time password. The server will automatically determine which type of password it has been given and attempt to authenticate accordingly. See skey() for more information on S/Key authentication. S/Key is a Trademark of Bellcore.

•

The login name must be allowed based on the information in ftpusers(5) .

•

The user must have a standard shell returned by getusershell(3) . If the user's shell field in the password database is empty, the shell is assumed to be /bin/sh .

•

If directed by the file ftpchroot() the session's root directory will be changed by chroot() to the directory specified in the ftpd.conf() directive (if set), or to the home directory of the user. However, the user must still supply a password. This feature is intended as a compromise between a fully anonymous account and a fully privileged account. The account should also be set up as for an anonymous account.

•

If the user name is or an anonymous FTP account must be present in the password file (user In this case the user is allowed to log in by specifying any password (by convention an email address for the user should be used as the password). The server performs a chroot() to the directory specified in the ftpd.conf() directive (if set), the -a anondir directory (if set), or to the home directory of the user. The server then performs a chdir() to the directory specified in the ftpd.conf() directive (if set), otherwise to / . If other restrictions are required (such as disabling of certain commands and the setting of a specific umask), then appropriate entries in ftpd.conf() are required. If the first character of the password supplied by an anonymous user is then the verbose messages displayed at login and upon a command are suppressed.

When displays various files back to the client (such as /etc/ftpwelcome and /etc/motd ) , various escape strings are replaced with information pertinent to the current connection.

The supported escape strings are:

Sy Escape

\&%c

Class name.

\&%C

Current working directory.

\&%E

Email address given with -e .

\&%L

Local hostname.

\&%M

Maximum number of users for this class. Displays if there's no limit.

\&%N

Current number of users for this class.

\&%R

Remote hostname.

\&%s

If the result of the most recent or was not print an

\&%S

If the result of the most recent or was not print an

\&%T

Current time.

\&%U

User name.

\&%\&%

A character.

In order that system security is not breached, it is recommended that the subtrees for the and accounts be constructed with care, following these rules (replace in the following directory names with the appropriate account name for users):

~ftp

Make the home directory owned by and unwritable by anyone.

~ftp/bin

Make this directory owned by and unwritable by anyone (mode 555). Generally any conversion commands should be installed here (mode 111).

~ftp/etc

Make this directory owned by and unwritable by anyone (mode 555). The files pwd.db (see passwd(5) ) and group (see group(5) ) must be present for the command to be able to display owner and group names instead of numbers. The password field in passwd() is not used, and should not contain real passwords. The file motd , if present, will be printed after a successful login. These files should be mode 444.

~ftp/pub

This directory and the subdirectories beneath it should be owned by the users and groups responsible for placing files in them, and be writable only by them (mode 755 or 775). They should be owned or writable by ftp or its group.

~ftp/incoming

This directory is where anonymous users place files they upload. The owners should be the user and an appropriate group. Members of this group will be the only users with access to these files after they have been uploaded; these should be people who know how to deal with them appropriately. If you wish anonymous FTP users to be able to see the names of the files in this directory the permissions should be 770, otherwise they should be 370. The following ftpd.conf() directives should be used: This will result in anonymous users being able to upload files to this directory, but they will not be able to download them, delete them, or overwrite them, due to the umask and disabling of the commands mentioned above.

~ftp/tmp

This directory is used to create temporary files which contain the error messages generated by a conversion or command. The owner should be the user The permissions should be 300. If you don't enable conversion commands, or don't want anonymous users uploading files here (see ~ftp/incoming above), then don't create this directory. However, error messages from conversion or commands won't be returned to the user. (This is the traditional behaviour.) Note that the ftpd.conf() directive can be used to prevent users uploading here.

To set up "ftp-only" accounts that provide only FTP , but no valid shell login, you can copy/link /sbin/nologin to /sbin/ftplogin , and enter /sbin/ftplogin to /etc/shells to allow logging-in via FTP into the accounts, which must have /sbin/ftplogin as login shell.

/etc/ftpchroot

List of normal users who should be chroot(2) ed.

/etc/ftpd.conf

Configure file conversions and other settings.

/etc/ftpusers

List of unwelcome/restricted users.

/etc/ftpwelcome

Welcome notice before login.

/etc/motd

Welcome notice after login.

/etc/nologin

If it exists, displayed and access is refused.

/var/run/ftpd.pids-CLASS

State file of logged-in processes for the class

/var/run/utmp

List of logged-in users on the system.

/var/log/wtmp

Login history database.

recognizes all commands in RFC 959 , follows the guidelines in RFC 1123 , recognizes all commands in RFC 2228 (although they are not supported yet), and supports the extensions from RFC 2389 , RFC 2428 and draft-ietf-ftpext-mlst-11 .

The command appeared in

Various features such as the ftpd.conf() functionality, RFC 2389 , and draft-ietf-ftpext-mlst-11 support was implemented in and later releases by Luke Mewburn <lukem@netbsd.org>.

The server must run as the super-user to create sockets with privileged port numbers (i.e, those less than IPPORT_RESERVED , which is 1024). If is listening on a privileged port it maintains an effective user id of the logged in user, reverting to the super-user only when binding addresses to privileged sockets. The -r option can be used to override this behaviour and force privileges to be permanently revoked; see below for more details.

may have trouble handling connections from scoped IPv6 addresses, or IPv4 mapped addresses IPv4 connection on AF_INET6 socket For the latter case, running two daemons, one for IPv4 and one for IPv6, will avoid the problem.

provides no restrictions on the command, and this can lead to security problems, as can be fooled into connecting to any service on any host. With the feature of the ftpd.conf(5) , commands with different host addresses, or TCP ports lower than IPPORT_RESERVED will be rejected. This also prevents from working. Use of this option is recommended, and enabled by default.

By default uses a port that is one less than the port it is listening on to communicate back to the client for the and commands, unless overridden with -P dataport . As the default port for (21) is a privileged port below IPPORT_RESERVED , retains the ability to switch back to root privileges to bind these ports. In order to increase security by reducing the potential for a bug in providing a remote root compromise, will permanently drop root privileges if one of the following is true:

•

is running on a port greater than IPPORT_RESERVED and the user has logged in as a or user.

•

was invoked with -r .

Don't create ~ftp/tmp if you don't want anonymous users to upload files there. That directory is only necessary if you want to display the error messages of conversion commands to the user. Note that if uploads are disabled with the ftpd.conf() directive then this directory cannot be abused by the user in this way, so it should be safe to create.