Provided by: ftpd-ssl_0.17.36+0.3-2.2build1_amd64 
NAME
ftpd — Internet File Transfer Protocol server
SYNOPSIS
ftpd [-AdDhlMnPSU] [-T maxtimeout] [-t timeout] [-u mask] [-z debug] [-z debug=file] [-z certsok]
[-z certrequired] [-z secure] [-z ssl] [-z verify=flags] [-z cacert=cafile] [-z cert=certfile]
[-z key=keyfile] [-z cipher=list] [-z legacy]
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:
-4 Use IPv4 addressing only. The default is to offer service for both families, IPv6 and IPv4.
-6 Only provide IPv6 addressing capability.
-A Permit only anonymous ftp connections or accounts listed in /etc/ftpchroot. Other connection
attempts are refused. This option is no longer effective if PAM is enabled. Please refer to the
README file for instructions to doing this with PAM.
-d Debugging information is written to the syslog using LOG_FTP.
-D With this option set, ftpd will detach and become a daemon, accepting connections on the FTP port
and forking child processes to handle them. This has lower overhead than starting ftpd from
inetd(8) and is thus useful on busy servers to reduce load.
-h The server will use data ports in the high port range for passive connections. This range is
defined by the IPPORT_HIFIRSTAUTO and IPPORT_HILASTAUTO defines in <netinet/in.h>. In OpenBSD
they are set to 49152 and 65535 respectively.
-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.
-M Enables multihomed mode. Instead of simply using ~ftp for anonymous transfers, a directory
matching the fully qualified name of the IP number the client connected to, and located inside
~ftp is used instead.
-n Use numeric IP addresses in logs instead of doing hostname lookup.
-P Permit illegal port numbers or addresses for PORT command initiated connects. By default ftpd(8)
violates the RFC and thus constrains the PORT command to non-reserved ports and requires it use
the same source address as the connection came from. This prevents the "FTP bounce attack"
against services on both the local machine and other local machines.
-S With this option set, ftpd logs all anonymous transfers to the file /var/log/ftpd when this file
exists.
-U Each concurrent ftp(1) session is logged to the file /var/run/utmp, making them visible to
commands such as who(1). This option at present is unsupporte and will always silently fail.
-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 Change the default umask from 027 to mask.
-z SSL-parameter
This option is only valid if ftpd has been built with SSL (Secure Socket Layer) support.
secure Don't fall back to unencrypted mode, that is without SSL, if the client is not
explicitly asking for SSL mode. In this server mode ftpd only accepts connections
from SSL enhanced FTP clients with an option similar to -z secure in active use.
ssl Negotiate SSL at first, then fall back to legacy FTP protocol.
nossl, !ssl
switch off SSL negotiation
debug Enable SSL related debugging. Useless in non-daemon mode.
debug=file Direct the debugging output to file.
certsok Look username up in /etc/ssl.users. The format of this file is lines of this form:
user1,user2:/C=US/...
where user1 and user2 are usernames. If the client certificate is valid,
authenticate with any password. Use a command openssl x509 -noout -subject to extract
the needed fields, all of which are needed.
certrequired
Client certificate is mandatory and the user must be matched to the corresponding
subject identifier listed in /etc/ssl.users.
verify=int Set the SSL verify flags (use combinations of SSL_VERIFY_* from openssl/ssl.h ).
cacert=ca_file
Use the CA certificates stored in ca_file to verify the identity of the peer client.
The subject names found herein are given to the client for whatever use they may
present. A clever client software is able to choose its identity hinted by this
list.
cert=cert_file
Use the certificate(s) in cert_file instead of the default location
/etc/ftpd-ssl/ftpd.pem. This is a PEM formatted file. The first certificate
identifies the server and the rest of the chain is used for verification purposes
while talking to the peer client.
key=key_file
Use the key stored in key_file, should the certificate file not contain the required
private key.
cipher=ciph_list
Set the preferred ciphers to ciph_list. See openssl/ssl.h for more information).
legacy This is a compatibility option, which activates a work around during verification,
which the legacy code depended on. It should not be used now that chains and CA
lists are available, but is introduced to ease the transition to the better
implementation.
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. If the file .message exists in a directory,
ftpd prints it when that directory is entered.
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
EPRT specify data connection port, either IPv4 or IPv6
EPSV ask for a server port for fetching data
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 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.
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 five rules.
1. 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. If the user has an S/Key key, the response from a successful USER command will
include an S/Key challenge. The client may choose to respond with a PASS command giving either
a standard password or an S/Key one-time password. The server will automatically determine
which type of password it has been given and attempt to authenticate accordingly. See skey(1)
for more information on S/Key authentication. S/Key is a Trademark of Bellcore.
2. The login name must not appear in the file /etc/ftpusers.
3. The user must have a standard shell returned by getusershell(3).
4. 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.
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 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 (mode 555).
~ftp/bin Make this directory owned by “root” and unwritable by anyone (mode 511). This directory
is required, and should contain at least a statically linked copy of ls(1.) Any programs
in this directory should be mode 111 (executable only).
~ftp/etc Make this directory owned by “root” and unwritable by anyone (mode 511). 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/lib Make this directory owned by “root” and unwritable by anyone (mode 511). The libraries
ld-linux.so.2 and libc.so.6 (or whatever your ls command is linked to) must be present.
In order to read passwd(5) and group(5), the library libnss_files.so.2 is also needed.
Note that if you're using a 2.2.* or later Linux kernel, ld-linux.so.2 must be executable
as well as readable (555). All other files should be mode 444.
~ftp/pub Make this directory mode 555 and owned by “root”. This is traditionally where publically
accessible files are stored for download.
FILES
/etc/ftpusers List of unwelcome/restricted 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.
/var/run/utmp List of users on the system.
/var/log/ftpd Log file for anonymous transfers.
/etc/ftpd-ssl/ftpd.pem
Default certificate and key for SSL authentication.
/etc/ssl.users List of trusted users and their subject identifiers.
ENVIRONMENT
Ftpd accesses a single environment variable:
SSL_CIPHER containing a list of acceptable cipher combinations.
SEE ALSO
ftp(1), skey(1), who(1), getusershell(3), ftpusers(5), syslogd(8)
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.
Linux NetKit (0.17) September 14, 1999 FTPD(8)