heimdal-ftpd man page

ftpd — Internet File Transfer Protocol server

Synopsis

ftpd [-a authmode] [-dilvU] [-g umask] [-p port] [-T maxtimeout] [-t timeout] [--gss-bindings] [-I | --no-insecure-oob] [-u default umask] [-B | --builtin-ls] [--good-chars=string]

Description

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:

-a
Select the level of authentication required. Kerberised login can not be turned off. The default is to only allow kerberised login. Other possibilities can be turned on by giving a string of comma separated flags as argument to -a. Recognised flags are:
plain
Allow logging in with plaintext password. The password can be a(n) OTP or an ordinary password.
otp
Same as plain, but only OTP is allowed.
ftp
Allow anonymous login.

The following combination modes exists for backwards compatibility:

none
Same as plain,ftp.
safe
Same as ftp.
user
Ignored.
-d
Debugging information is written to the syslog using LOG_FTP.
-g
Anonymous users will get a umask of umask.
--gss-bindings
require the peer to use GSS-API bindings (ie make sure IP addresses match).
-i
Open a socket and wait for a connection. This is mainly used for debugging when ftpd isn't started by inetd.
-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.
-p
Use port (a service name or number) instead of the default ftp/tcp.
-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).
-u
Set the initial umask to something else than the default 027.
-U
In previous versions of ftpd, when a passive mode client requested a data connection to the server, the server would use data ports in the range 1024..4999. Now, by default, if the system supports the IP_PORTRANGE socket option, the server will use data ports in the range 49152..65535. Specifying this option will revert to the old behavior.
-v
Verbose mode.
-B, --builtin-ls
use built-in ls to list files
--good-chars=string
allowed anonymous upload filename chars
-I --no-insecure-oob
don't allow insecure out of band. Heimdal ftp clients before 0.6.3 doesn't support secure oob, so turning on this option makes them no longer work.

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 commands are specified by RFC2228.

AUTH authentication/security mechanism
ADAT authentication/security data
PROT data channel protection level
PBSZ protection buffer size
MIC integrity protected command
CONF confidentiality protected command
ENC privacy protected command
CCC clear command channel

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

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)
FIND quickly find a specific file with GNU locate(1).
HELP give help information.

The following Kerberos related site commands are understood.

KAUTH obtain remote tickets.
KLIST show remote tickets

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 use the metacharacters “*?[]{}~”.

Ftpd authenticates users according to these rules.

  1. If Kerberos authentication is used, the user must pass valid tickets and the principal must be allowed to login as the remote user.
  2. The login name must be in the password data base, and not have a null password (if Kerberos is used the password field is not checked). In this case a password must be provided by the client before any file operations may be performed. If the user has an OTP key, the response from a successful USER command will include an OTP challenge. The client may choose to respond with a PASS command giving either a standard password or an OTP one-time password. The server will automatically determine which type of password it has been given and attempt to authenticate accordingly. See otp(1) for more information on OTP authentication.
  3. The login 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 appears in the file /etc/ftpchroot the session's root will be changed to the user's login directory by chroot(2) as for an “anonymous” or “ftp” account (see next item). However, the user must still supply a password. This feature is intended as a compromise between a fully anonymous account and a fully privileged account. The account should also be set up as for an anonymous account.
  6. 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, consider following these guidelines for anonymous ftp.

In general all files should be owned by “root”, and have non-write permissions (644 or 755 depending on the kind of file). No files should be owned or writable by “ftp” (possibly with exception for the ~ftp/incoming, as specified below).

~ftp
The “ftp” homedirectory should be owned by root.
~ftp/bin
The directory for external programs (such as ls(1)). These programs must either be statically linked, or you must setup an environment for dynamic linking when running chrooted. These programs will be used if present:
ls
Used when listing files.
compress
When retrieving a filename that ends in .Z, and that file isn't present, ftpd will try to find the filename without .Z and compress it on the fly.
gzip
Same as compress, just with files ending in .gz.
gtar
Enables retrieval of whole directories as files ending in .tar. Can also be combined with compression. You must use GNU Tar (or some other that supports the -z and -Z flags).
locate
Will enable ``fast find'' with the SITE FIND command. You must also create a locatedb file in ~ftp/etc.
~ftp/etc
If you put copies of the passwd(5) and group(5) files here, ls will be able to produce owner names rather than numbers. Remember to remove any passwords from these files.

The file motd, if present, will be printed after a successful login.

~ftp/dev
Put a copy of /dev/null(7) here.
~ftp/pub
Traditional place to put whatever you want to make public.

If you want guests to be able to upload files, create a ~ftp/incoming directory owned by “root”, and group “ftp” with mode 730 (make sure “ftp” is member of group “ftp”). The following restrictions apply to anonymous users:

Files

/etc/ftpusers
Access list for users.
/etc/ftpchroot
List of normal users who should be chroot'd.
/etc/ftpwelcome
Welcome notice.
/etc/motd
Welcome notice after login.
/etc/nologin
Displayed and access refused.
~/.klogin
Login access for Kerberos.

See Also

ftp(1), otp(1), getusershell(3), ftpusers(5), syslogd(8)

Standards

RFC 959
FTP PROTOCOL SPECIFICATION
RFC 1938
OTP Specification
RFC 2228
FTP Security Extensions.

Bugs

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.

Info

July 19, 2003