NAME¶
ftpd —
Internet File Transfer Protocol
server
SYNOPSIS¶
ftpd |
[-AdDhlMnPSU]
[-T
maxtimeout]
[-t
timeout]
[-u mask]
[-z debug]
[-z
certsok]
[-z
certrequired]
[-z
secure]
[-z
verify=flags]
[-z
cert=certfile]
[-z
key=keyfile]
[-z
ciper=list] |
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.
- debug
- Enable SSL related debugging.
- ssl
- Negotiate SSL at first, then use ftp protocol. In this
mode ftpd only accepts connections from SSL enhanced ftp with option
-z ssl. (Not yet implemented)
- nossl,
!ssl
- switch off SSL negotiation
- 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 client certificate is valid, authenticate without
password.
- certrequired
- client certificate is mandatory
- secure
- Don't switch back to unencrypted mode (no SSL) if SSL
is not available.
- verify=int
- Set the SSL verify flags (SSL_VERIFY_* in
ssl/ssl.h ).
- cert=cert_file
- Use the certificate(s) in
cert_file.
- key=key_file
- Use the key(s) in key_file.
- cipher=ciph_list
- Set the preferred ciphers to
ciph_list. (See ssl/ssl.h
).
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.
- 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.
- 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 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.
- 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.
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.