ftpd - Internet File Transfer Protocol server

ftpd [ -d ] [ -v ] [ -l ] [ -t timeout ] [ -T maxtimeout ] [ -a ] [ -A ] [ -L ] [ -i ] [ -I ] [ -o ] [ -p ctrlport ] [ -P dataport ] [ -q ] [ -Q ] [ -r rootdir ] [ -R ] [ -s ] [ -S ] [ -u umask ] [ -V ] [ -w ] [ -W ] [ -X ]

Ftpd is the 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(5).

The -V option causes the program to display copyright and version information, then terminate.

If the -d or -v option is specified, debugging information is written to the syslog.

If the -l option is specified, each ftp session is logged in the syslog.

The ftp server will timeout an inactive session after 15 minutes. If the -t option is specified, the inactivity timeout period will be set to timeout seconds. 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.

If the -a option is specified, the use of the ftpaccess(5) configuration file is enabled.

If the -A option is specified, use of the ftpaccess(5) configuration file is disabled. This is the default.

If the -L option is specified, commands sent to the ftpd(8) server will be logged to the syslog. The -L option is overridden by the use of the ftpaccess(5) file. If the -L flag is used, command logging will be on by default as soon as the ftp server is invoked. This will cause the server to log all USER commands, which if a user accidentally enters a password for that command instead of the username, will cause passwords to be logged via syslog.

If the -i option is specified, files received by the ftpd(8) server will be logged to the xferlog(5). The -i option is overridden by the use of the ftpaccess(5) file.

The -I option disables the use of RFC931 (AUTH/ident) to attempt to determine the username on the client.

If the -o option is specified, files transmitted by the ftpd(8) server will be logged to the xferlog(5). The -o option is overridden by the use of the ftpaccess(5) file. If the -X option is specified, the output created by the -i and -o options is not saved to the xferlog file but saved via syslog so you can collect output from several hosts on one central loghost.

If the -u option is specified, the default umask is set to umask.

If the -W option is specified user logins are not recorded in the wtmp file. The default ( -w ) is to record every login and logout.

The -s and -S options place the daemon in standalone operation mode. The -S option runs the daemon in the background and is useful in startup scripts during system initialization (ie., in rc.local). The -s option leaves the daemon in foreground and is useful when running from init (ie., /etc/inittab).

The -p and -P options override the port numbers used by the daemon. Normally, the daemon determines the port numbers by looking in /etc/services for "ftp" and "ftp-data". If there is no /etc/services entry for "ftp-data" and the -P option is not specified, the daemon uses the port just prior to the control connection port. The -p option is only available if running as a standalone daemon.

The -q and -Q options deterine whether the daemon uses the PID files. These files are required by the limit directive to determine the number of current users in each access class. Disabling the use of the PID files disables user limits. The default ( -q ) is to use the PID files. Specify -Q when testing the server as a normal user when access permissions prevent the use of the PID files. Large, busy sites which do not wish to impose limits on the number of concurrent users may also consider disabling the PID files.

The -r option instructs the daemon to chroot(2) to the specified rootdir immedeately upon loading. This can improve system security by limiting the files which may be damaged should a breakin occur through the daemon. Set is much like anonymous FTP, with additional files needed which vary from system to system.

When started with -R the daemon will not honour the REST command, possibly preventing "download managers" from hogging your bandwidth.

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

Request	Description
ABOR	abort previous command
ACCT	specify account (ignored)
ALLO	allocate storage (vacuously)
APPE	append to a file
CDUP	change to parent of current working directory
CWD	change working directory
DELE	delete a file
HELP	give help information
LIST	give list files in a directory (``ls -lgA'')
MKD	make a directory
MDTM	show last modification time of file
MODE	specify data transfer mode
NLST	give name list of files in directory 
NOOP	do nothing
PASS	specify password
PASV	prepare for server-to-server transfer
PORT	specify data connection port
PWD	print the current working directory
QUIT	terminate session
REST	restart incomplete transfer
RETR	retrieve a file
RMD	remove a directory
RNFR	specify rename-from file name
RNTO	specify rename-to file name
SITE	non-standard commands (see next section)
SIZE	return size of file
STAT	return status of server
STOR	store a file
STOU	store a file with a unique name
STRU	specify data transfer structure
SYST	show operating system type of server system
TYPE	specify data transfer type
USER	specify user name
XCUP	change to parent of current working directory (deprecated)
XCWD	change working directory (deprecated)
XMKD	make a directory (deprecated)
XPWD	print the current working directory (deprecated)
XRMD	remove a directory (deprecated)

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

Request	Description
UMASK	change umask. E.g. SITE UMASK 002
IDLE	set idle-timer. E.g. SITE IDLE 60
CHMOD	change mode of a file. E.g. SITE CHMOD 755 filename
HELP	give help information. E.g. SITE HELP
NEWER	list files newer than a particular date
MINFO	like SITE NEWER, but gives extra information
GROUP	request special group access. E.g. SITE GROUP foo
GPASS	give special group access password. E.g. SITE GPASS bar
EXEC	execute a program.  E.g. SITE EXEC program params

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 ``globbing'' conventions used by csh(1). This allows users to utilize the metacharacters ``*?[]{}~''.

Ftpd authenticates users according to four rules.

1)

The user name must be in the password data base, /etc/passwd, or whatever is appropriate for the operating system, and the password must not be null. In this case a password must be provided by the client before any file operations may be performed.

2)

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

3)

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

4)

If the user name is ``anonymous'' or ``ftp'', an anonymous ftp account must be present in the password 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).

In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot(2) command to the home directory of the ``ftp'' user. In order that system security is not breached, it is recommended that the ``ftp'' subtree be constructed with care; the following rules are recommended.

~ftp)

Make the home directory owned by super-user and unwritable by anyone.

~ftp/bin)

Make this directory owned by the super-user and unwritable by anyone. The program ls(1) must be present to support the list command. This program should have mode 111.

~ftp/etc)

Make this directory owned by the super-user and unwritable by anyone. The files passwd(5) and group(5) must be present for the ls command to be able to produce owner names rather than numbers. Depending on the operating system, there may be other required files. Check your manual page for the getpwent(3) library routine. The password field in passwd is not used, and should not contain real encrypted passwords. These files should be mode 444 and owned by the super-user. Don't use the system's /etc/passwd file as the password file or the system's /etc/group file as the group file in the ~ftp/etc directory.

~ftp/pub)

Create a subdirectory in ~ftp/pub with the appropriate mode (777 or 733) if you want to allow normal users to upload files.

The authentication mechanism used by ftpd is determined by the ``auth-ftp'' entry in the /etc/login.conf file (see login.conf(5)) that matches the users class. If there is no ``auth-ftp'' entry for the class, the normal ``auth'' entry will be used instead. An alternate authentication mechanism may be specified by appending a colon (``:'') followed by the authentication style, i.e. ``joe:skey''.

There are some extensions to the FTP server such that if the user specifies a filename (when using a RETRIEVE command) such that:

 True Filename  Specified Filename  Action
 -------------  ------------------  -----------------------------------
 <filename>.Z   <filename>          Decompress file before transmitting
 <filename>     <filename>.Z        Compress <filename> before 
                                            transmitting
 <filename>     <filename>.tar      Tar <filename> before transmitting
 <filename>     <filename>.tar.Z    Tar and compress <filename> before
                                            transmitting

Also, the FTP server will attempt to check for valid e-mail addresses and chide the user if he doesn't pass the test. For users whose FTP client will hang on "long replies" (i.e. multiline responses), using a dash as the first character of the password will disable the server's lreply() function.

The FTP server can also log all file transmission and reception, keeping the following information for each file transmission that takes place.

Mon Dec  3 18:52:41 1990 1 wuarchive.wustl.edu 568881 /files.lst.Z a _ o a chris@wugate.wustl.edu ftp 0 *

%.24s %d %s %d %s %c %s %c %c %s %s %d %s 1 2 3 4 5 6 7 8 9 10 11 12 13

1 current time in the form DDD MMM dd hh:mm:ss YYYY 2 transfer time in seconds 3 remote host name 4 file size in bytes 5 name of file 6 transfer type (a>scii, b>inary) 7 special action flags (concatenated as needed): C file was compressed U file was uncompressed T file was tar'ed _ no action taken 8 file was sent to user (o>utgoing) or received from user (i>ncoming) 9 accessed anonymously (r>eal, a>nonymous, g>uest) -- mostly for FTP 10 local username or, if guest, ID string given (anonymous FTP password) 11 service name ('ftp', other) 12 authentication method (bitmask) 0 none 1 RFC931 Authentication 13 authenticated user id (if available, '*' otherwise)

ftp(1), getusershell(3), syslogd(8), ftpaccess(5), xferlog(5), umask(2)

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

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.