NAME¶
ftpd
—
Internet File Transfer Protocol server
SYNOPSIS¶
ftpd |
[ -AdDhlMnPSU ]
[-T
maxtimeout ]
[-t
timeout ]
[-u
mask ] |
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.
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.