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).
Available options:
- -d
-
Debugging information is written to the syslog using LOG_FTP.
- -l
-
Each successful and failed
ftp(1)
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.
- -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).
The file
/etc/nologin can be used to disable ftp access.
If the file exists,
Ftpd displays it and exits.
If the file
/etc/ftpwelcome exists,
Ftpd prints it before issuing the
``ready'' message.
If the file
/etc/motd exists,
Ftpd prints it after a successful login.
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.
- 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 changeumask,e.g.``SITEUMASK002''
-
- IDLE setidle-timer,e.g.``SITEIDLE60''
-
- CHMOD changemodeofafile,e.g.``SITECHMOD755filename''
-
- HELP givehelpinformation.
-
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 three rules.
-
The login name must be in the password data base,
/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 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 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 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(2)
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, following these rules:
- ~ftp
-
Make the home directory owned by
``root'' and unwritable by anyone.
- ~ftp/bin
-
Make this directory owned by
``root'' and unwritable by anyone (mode 555).
The program
ls(1)
must be present to support the list command.
This program should be mode 111.
- ~ftp/etc
-
Make this directory owned by
``root'' and unwritable by anyone (mode 555).
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 passwords.
The file
motd, if present, will be printed after a successful login.
These files should be mode 444.
- ~ftp/pub
-
Make this directory mode 777 and owned by
``ftp''. Guests
can then place files which are to be accessible via the anonymous
account in this directory.
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.