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

Select the level of authentication required. Kerberised login can not be turned off. The default is to only allow kerberised login. Other possibilities can be turned on by giving a string of comma separated flags as argument to -a . Recognised flags are:

plain

Allow logging in with plaintext password. The password can be a(n) OTP or an ordinary password.

otp

Same as plain , but only OTP is allowed.

ftp

Allow anonymous login.

The following combination modes exists for backwards compatibility:

none

Same as plain,ftp .

safe

Same as ftp .

user

Ignored.

-d

Debugging information is written to the syslog using LOG_FTP.

-g

Anonymous users will get a umask of umask .

-i

Open a socket and wait for a connection. This is mainly used for debugging when ftpd isn't started by inetd.

-l

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

-p

Use port (a service name or number) instead of the default ftp/tcp .

-T

A client may also request a different timeout period; the maximum period allowed may be set to timeout seconds with the -T option. The default limit is 2 hours.

-t

The inactivity timeout period is set to timeout seconds (the default is 15 minutes).

-u

Set the initial umask to something else than the default 027.

-U

In previous versions of ftpd , when a passive mode client requested a data connection to the server, the server would use data ports in the range 1024..4999. Now, by default, if the system supports the IP_PORTRANGE socket option, the server will use data ports in the range 49152..65535. Specifying this option will revert to the old behavior.

-v

Verbose mode.

Xo

-B , --builtin-ls use built-in ls to list files

Xo

--good-chars= Ns string allowed anonymous upload filename chars

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, prints it after a successful login.

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

Request Ta 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

HELP Ta give help information

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

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

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 commands are specified by RFC2228.

AUTH Ta authentication/security mechanism

ADAT Ta authentication/security data

PROT Ta data channel protection level

PBSZ Ta protection buffer size

MIC Ta integrity protected command

CONF Ta confidentiality protected command

ENC Ta privacy protected command

CCC Ta clear command channel

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

UMASK Ta change umask, (e.g.

SITE UMASK 002 )

IDLE Ta set idle-timer, (e.g.

SITE IDLE 60 )

CHMOD Ta change mode of a file (e.g.

SITE CHMOD 755 filename )

FIND Ta quickly find a specific file with GNU

locate(1) .

HELP Ta give help information.

The following Kerberos related site commands are understood.

KAUTH Ta obtain remote tickets.

KLIST Ta show remote tickets

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.

The ftp server will abort an active file transfer only when the ABOR 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 STAT command is received during a data transfer, preceded by a Telnet IP and Synch, transfer status will be returned.

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

Ftpd authenticates users according to these rules.

•

If Kerberos authentication is used, the user must pass valid tickets and the principal must be allowed to login as the remote user.

•

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

•

The login name must not appear in the file /etc/ftpusers .

•

The user must have a standard shell returned by getusershell(3) .

•

If the user name appears in the file /etc/ftpchroot the session's root will be changed to the user's login directory by chroot() as for an or account (see next item). 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).

In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot() to the home directory of the user. In order that system security is not breached, it is recommended that the subtree be constructed with care, consider following these guidelines for anonymous ftp.

In general all files should be owned by and have non-write permissions (644 or 755 depending on the kind of file). No files should be owned or writable by (possibly with exception for the ~ftp/incoming , as specified below).

~ftp

The homedirectory should be owned by root.

~ftp/bin

The directory for external programs (such as ls(1) ) . These programs must either be statically linked, or you must setup an environment for dynamic linking when running chrooted. These programs will be used if present:

ls

Used when listing files.

compress

When retrieving a filename that ends in .Z , and that file isn't present, will try to find the filename without .Z and compress it on the fly.

gzip

Same as compress, just with files ending in .gz .

gtar

Enables retrieval of whole directories as files ending in .tar . Can also be combined with compression. You must use GNU Tar (or some other that supports the -z and -Z flags).

locate

Will enable ``fast find'' with the SITE FIND command. You must also create a locatedb file in ~ftp/etc .

~ftp/etc

If you put copies of the passwd() and group() files here, ls will be able to produce owner names rather than numbers. Remember to remove any passwords from these files. The file motd , if present, will be printed after a successful login.

~ftp/dev

Put a copy of /dev/null() here.

~ftp/pub

Traditional place to put whatever you want to make public.

If you want guests to be able to upload files, create a ~ftp/incoming directory owned by and group with mode 730 (make sure is member of group The following restrictions apply to anonymous users:

•

Directories created will have mode 700.

•

Uploaded files will be created with an umask of 777, if not changed with the -g option.

•

These command are not accessible: DELE , RMD , RNTO , RNFR , SITE UMASK , and SITE CHMOD .

•

Filenames must start with an alpha-numeric character, and consist of alpha-numeric characters or any of the following: + (plus), - (minus), = (equal), _ (underscore), . (period), and , (comma).

/etc/ftpusers

Access list for users.

/etc/ftpchroot

List of normal users who should be chroot'd.

/etc/ftpwelcome

Welcome notice.

/etc/motd

Welcome notice after login.

/etc/nologin

Displayed and access refused.

~/.klogin

Login access for Kerberos.

RFC 959

FTP PROTOCOL SPECIFICATION

RFC 1938

OTP Specification

RFC 2228

FTP Security Extensions.

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

The command appeared in