NAME¶
ftpd - DARPA Internet File Transfer Protocol server
SYNOPSIS¶
ftpd [
-A |
-a] [
-C] [
-c] [
-d]
[
-E] [
-l] [
-v] [
-T maxtimeout] [
-t
timeout] [
-p port] [
-U ftpusers-file]
[
-u umask] [
-r realm-file] [
-s
srvtab] [
-w{
ip|
maxhostlen[
,{
striplocal|
nostriplocal}]}]
DESCRIPTION¶
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).
Available options:
- -A
- Connections are only allowed for users who can authenticate
via the ftp AUTH mechanism. (Anonymous ftp may also be allowed if it is
configured.) Ftpd will ask the user for a password if one is
required.
- -a
- Connections are only allowed for users who can authenticate
(via the ftp AUTH mechanism) and who are authorized to connect to the
named account without a password. (Anonymous ftp may also be allowed if it
is configured.)
- -C
- Non-anonymous users need local credentials (for example, to
authenticate to remote fileservers), and so they should be prompted for a
password unless they forwarded credentials as part of authentication.
- -c
- Allow the CCC (Clear Command Channel) command to be used.
This allows less secure connections, and should probably only be used when
debugging.
- -d
- Debugging information is written to the syslog. (Identical
to -v)
- -E
- Don't allow passwords to be typed across unencrypted
connections.
- -l
- Each ftp(1) session is logged in the syslog. If this
flag appears twice, additional information about operations performed
(such as files retrieved, directories created, etc.) will be logged via
syslog. If it appears three times, some other statistics such as the
number of bytes transferred will be logged via syslog as well.
- -v
- Debugging information is written to the syslog. (Identical
to -d)
- -T maxtimeout
- A client may request a maximum timeout period allowed set
to timeout seconds with the -T option. The default limit is
2 hours. This is different from the normal inactivity timeout specified by
the -t option (see below).
- -t timeout
- The inactivity timeout period is set to timeout
seconds (the default is 15 minutes).
- -p port
- Run as a server and accept a connection on port.
Normally the ftp server is invoked by inetd(8).
- -U ftpusers-file
- Sets the full path and name of the ftpusers file to
use. The default value is normally /etc/ftpusers.
- -u umask
- Sets the umask for the ftpd process. The default value is
normally 027.
- -w
{ip|maxhostlen[,{striplocal|
nostriplocal}]}
- Controls the form of the remote hostname passed to
login(1). Specifying ip results in the numeric IP address always
being passed to login(1). Specifying a number, maxhostlen, sets the
maximum length of the hostname passed to login(1) before it will be passed
as a numeric IP address. If maxhostlen is 0, then the system
default, as determined by the utmp or utmpx structures, is used. The
nostriplocal and striplocal options, which must be preceded
by a comma, control whether or not the local host domain is stripped from
the remote hostname. By default, the equivalent of striplocal is in
effect.
The ftp server currently supports the following ftp requests; case is not
distinguished.
- Request
- Description
- ABOR
- abort previous command
- ACCT
- specify account (ignored)
- ADAT
- send an authentication protocol message
- ALLO
- allocate storage (vacuously)
- APPE
- append to a file
- AUTH
- specify an authentication protocol to be performed
- CCC
- set the command channel protection mode to
"Clear" (no protection). Only available if the -c
command-line option was given.
- CDUP
- change to parent of current working directory
- CWD
- change working directory
- DELE
- delete a file
- ENC
- send a privacy and integrity protected command (given in
argument)
- HELP
- give help information
- LIST
- give list files in a directory (``ls -lgA'')
- MIC
- send an integrity protected command (given in argument)
- 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
- PBSZ
- specify a protection buffer size
- PORT
- specify data connection port
- PROT
- specify a protection level under which to protect data
transfers
- 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
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 the following rules:
-
1.
- The user name must be in the password data base,
/etc/passwd.
-
2.
- An AUTH command must be accepted, the
ensuing authentication protocol (conducted via ADAT
commands and replies) must successfully complete, and the authenticated
user must permitted access. Otherwise, a valid password which is not null
must be provided by the client.
-
3.
- The user name must not appear in the file
/etc/ftpusers.
-
4.
- The user must have a standard shell returned by
getusershell(3).
-
5.
- 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 ``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.
If an
ADAT command succeeds, the control channel must be either
integrity or privacy protected. In this case, the
MIC and
ENC commands are the only commands allowed over the control
channel. The argument to the
MIC command is a base 64 encoded
string which, when decoded, is an ftp command integrity protected with a
cryptographic checksum. The argument to the
ENC command is a
base 64 encoded string which, when decoded, is an ftp command privacy and
integrity protected with encryption.
If an
ADAT command succeeds, ftp replies will also be either
integrity or privacy protected.
If an
ADAT command succeeds, the data channel can also be
integrity or privacy protected. The
PROT command accepts S for
integrity and P for privacy protection. Unless an
ADAT command
succeeds, the only protection level accepted by the
PROT
command is C (clear).
SEE ALSO¶
ftp(1),
getusershell(3),
syslogd(8)
Lunt, S. J., FTP Security Extensions, Internet Draft, November 1993.
BUGS¶
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.
HISTORY¶
The
ftpd command appeared in 4.2BSD.