ftpd - DARPA Internet File Transfer Protocol server
ftpd [ -d ] [ -l ] [ -ttimeout ] [ -Tmaxtimeout ] [ -a ] [ -A ] [ -L ] [ -i ] [ -I ] [ -o ] [ -O ]
Ftpd is the DARPA 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) .
If the -d 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.
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.
If the -o option is specified, files transmitted by the ftpd(8) server will be logged to the syslog. The -o option is overridden by the use of the ftpaccess(5) file.
The ftp server currently supports the following ftp requests; case is not distinguished.
The following non-standard or UNIX specific 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.
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.
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 ``ftp'' 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.
The password field in passwd is not used, and
should not contain real encrypted passwords. These
files should be mode 444.
~ftp/pub)
Make this directory mode 777 and owned by ``ftp''.
Users should then place files which are to be
accessible via the anonymous account in this directory.
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
Also, the FTP server will attempt to check for valid email 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):
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.