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10 January 1995


Support for One-Time Passwords


opieftpd - File Transfer Protocol server that uses OPIE authentication


opieftpd [-d] [-l] [-t timeout ] [-T maxtimeout ] [-u umask ]


opieftpd 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).


-d Debugging information is written to the system logs.
-l Each ftp(1) session is logged in the system logs.
-t The inactivity timeout period is set to timeout seconds (the default is 15 minutes).
-T A client may also request a different timeout period; the maximum period allowed may be set to maxtimeout seconds with the -T option. The default limit is 2 hours. -u Set the default umask value to umask.


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 a list of files in a directory
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 file)
HELP      give help information (e.g. SITE HELP)
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. opieftpd interprets file names according to the globbing conventions used by csh(1). This allows users to utilize the metacharacters *?[]{}~.
opieftpd authenticates users according to three rules:
The user 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 user 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, this is given as the client host’s name).
In the last case, opieftpd 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.
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.
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(1) 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.
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.


The anonymous account is inherently dangerous and should avoided when possible. In opieftpd, it is a compile-time option that should be disabled if it is not being used. 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 scrutinized, but are possibly incomplete.


The ftpd command appeared in 4.2BSD.


Originally written for BSD, ftpd was modified at NRL by Randall Atkinson, Dan McDonald, and Craig Metz to support OTP authentication.


OPIE is discussed on the Bellcore "S/Key Users" mailing list. To join, send an email request to:
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