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
When -D is specified, bind to IPv4 addresses only.
-6
When -D is specified, bind to IPv6 addresses only.
-a anondir
Define
anondir as the directory to
chroot(2) into for anonymous logins. Default is the home directory for the ftp user. This can also be specified with the
ftpd.conf(5) chroot directive.
-C user[@host]
Check whether
user (as if connecting from
host, if provided) would be granted access under the restrictions given in
ftpusers(5), and exit without attempting a connection.
ftpd exits with an exit code of 0 if access would be granted, or 1 otherwise. This can be useful for testing configurations.
-c confdir
Change the root directory of the configuration files from “
/etc” to
confdir. This changes the directory for the following files:
/etc/ftpchroot,
/etc/ftpusers,
/etc/ftpwelcome,
/etc/motd, and the file specified by the
ftpd.conf(5) limit directive.
-D
Run as daemon.
ftpd will listen on the default FTP port for incoming connections and fork a child for each connection. This is lower overhead than starting
ftpd from
inetd(8) and thus might be useful on busy servers to reduce load.
-d
Debugging information is written to the syslog using a facility of LOG_FTP.
-H
Equivalent to “-h `hostname`”.
-h hostname
Explicitly set the hostname to advertise as to
hostname. The default is the hostname associated with the IP address that
ftpd is listening on. This ability (with or without
-h), in conjunction with
-c confdir, is useful when configuring ‘virtual' FTP servers, each listening on separate addresses as separate names. Refer to
inetd.conf(5) for more information on starting services to listen on specific IP addresses.
-L xferlogfile
Log wu-ftpd style ‘xferlog' entries to xferlogfile.
-l
Each successful and failed FTP session is logged using syslog with a facility of LOG_FTP. If this option is specified more than once, the retrieve (get), store (put), append, delete, make directory, remove directory and rename operations and their file name arguments are also logged.
-n
Don't attempt translation of IP addresses to hostnames.
-P dataport
Use dataport as the data port, overriding the default of using the port one less that the port ftpd is listening on.
-Q
Disable the use of pid files for keeping track of the number of logged-in users per class. This may reduce the load on heavily loaded FTP servers.
-q
Enable the use of pid files for keeping track of the number of logged-in users per class. This is the default.
-r
Permanently drop root privileges once the user is logged in. The use of this option may result in the server using a port other than the (listening-port - 1) for
PORT style commands, which is contrary to the
RFC 959 specification, but in practice very few clients rely upon this behaviour. See
SECURITY CONSIDERATIONS below for more details.
-s
Require a secure authentication mechanism like Kerberos or S/Key to be used.
-U
Don't log each concurrent FTP session to /var/run/utmp. This is the default.
-u
Log each concurrent FTP session to
/var/run/utmp, making them visible to commands such as
who(1).
-V version
Use version as the version to advertise in the login banner and in the output of STAT and SYST instead of the default version information. If version is empty or ‘-' then don't display any version information.
-W
Don't log each FTP session to /var/log/wtmp.
-w
Log each FTP session to
/var/log/wtmp, making them visible to commands such as
last(1). This is the default.
-X
Log wu-ftpd style ‘xferlog' entries to the syslog, prefixed with “xferlog: ”, using a facility of
LOG_FTP. These syslog entries can be converted to a wu-ftpd style
xferlog file suitable for input into a third-party log analysis tool with a command similar to:
sed -ne 's/^.*xferlog: //p' /var/log/xferlog > wuxferlog
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 (under the chroot directory if applicable),
ftpd prints it after a successful login. This may be changed with the
ftpd.conf(5) directive
motd.
The
ftpd server currently supports the following FTP requests. The case of the requests is ignored.
ABOR
abort previous command
ACCT
specify account (ignored)
ALLO
allocate storage (vacuously)
CDUP
change to parent of current working directory
CWD
change working directory
EPSV
prepare for server-to-server transfer
EPRT
specify data connection port
FEAT
list extra features that are not defined in RFC 959
HELP
give help information
LIST
give list files in a directory (“ls -lA”)
LPSV
prepare for server-to-server transfer
LPRT
specify data connection port
MLSD
list contents of directory in a machine-processable form
MLST
show a pathname in a machine-processable form
MDTM
show last modification time of file
MODE
specify data transfer mode
NLST
give name list of files in directory
OPTS
define persistent options for a given command
PASV
prepare for server-to-server transfer
PORT
specify data connection port
PWD
print the current working directory
REST
restart incomplete transfer
RNFR
specify rename-from file name
RNTO
specify rename-to file name
SITE
non-standard commands (see next section)
STAT
return status of server
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
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.
CHMOD
change mode of a file, e.g. ``SITE CHMOD 755 filename''
HELP
give help information.
IDLE
set idle-timer, e.g. ``SITE IDLE 60''
RATEGET
set maximum get rate throttle in bytes/second, e.g. ``SITE RATEGET 5k''
RATEPUT
set maximum put rate throttle in bytes/second, e.g. ``SITE RATEPUT 5k''
UMASK
change umask, e.g. ``SITE UMASK 002''
The following FTP requests (as specified in
RFC 959 and
RFC 2228) are recognized, but are not implemented:
ACCT,
ADAT,
AUTH,
CCC,
CONF,
ENC,
MIC,
PBSZ,
PROT,
REIN, and
SMNT.
The
ftpd 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 “
*?[]{}~”.
User authentication
ftpd authenticates users according to five rules.
1.
The login name must be in the password data base,
passwd(5), 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 be allowed based on the information in
ftpusers(5).
3.
The user must have a standard shell returned by
getusershell(3). If the user's shell field in the password database is empty, the shell is assumed to be
/bin/sh. As per
shells(5), the user's shell must be listed with full path in
/etc/shells.
4.
If directed by the file
ftpchroot(5) the session's root directory will be changed by
chroot(2) to the directory specified in the
ftpd.conf(5) chroot directive (if set), or to the home directory of the user. This facility may also be triggered by enabling the boolean
ftp-chroot in
login.conf(5). 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).
The server performs a
chroot(2) to the directory specified in the
ftpd.conf(5) chroot directive (if set), the
-a anondir directory (if set), or to the home directory of the “ftp” user.
The server then performs a
chdir(2) to the directory specified in the
ftpd.conf(5) homedir directive (if set), otherwise to
/.
If other restrictions are required (such as disabling of certain commands and the setting of a specific umask), then appropriate entries in
ftpd.conf(5) are required.
If the first character of the password supplied by an anonymous user is “-”, then the verbose messages displayed at login and upon a
CWD command are suppressed.
Display file escape sequences
When
ftpd displays various files back to the client (such as
/etc/ftpwelcome and
/etc/motd), various escape strings are replaced with information pertinent to the current connection.
The supported escape strings are:
%C
Current working directory.
%E
Email address given with -e.
%M
Maximum number of users for this class. Displays “unlimited” if there's no limit.
%N
Current number of users for this class.
%s
If the result of the most recent “%M” or “%N” was not “1”, print an “s”.
%S
If the result of the most recent “%M” or “%N” was not “1”, print an “S”.
Setting up a restricted ftp subtree
In order that system security is not breached, it is recommended that the subtrees for the “ftp” and “chroot” accounts be constructed with care, following these rules (replace “ftp” in the following directory names with the appropriate account name for ‘chroot' users):
~ftp
Make the home directory owned by “root” and unwritable by anyone.
~ftp/bin
Make this directory owned by “root” and unwritable by anyone (mode 555). Generally any conversion commands should be installed here (mode 111).
~ftp/etc
Make this directory owned by “root” and unwritable by anyone (mode 555). The files
pwd.db (see
passwd(5)) and
group (see
group(5)) must be present for the
LIST command to be able to display owner and group names instead of numbers. The password field in
passwd(5) 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/pub
This directory and the subdirectories beneath it should be owned by the users and groups responsible for placing files in them, and be writable only by them (mode 755 or 775). They should not be owned or writable by ftp or its group.
~ftp/incoming
This directory is where anonymous users place files they upload. The owners should be the user “ftp” and an appropriate group. Members of this group will be the only users with access to these files after they have been uploaded; these should be people who know how to deal with them appropriately. If you wish anonymous FTP users to be able to see the names of the files in this directory the permissions should be 770, otherwise they should be 370.
The following
ftpd.conf(5) directives should be used:
modify guest off
umask guest 0707
upload guest on
This will result in anonymous users being able to upload files to this directory, but they will not be able to download them, delete them, or overwrite them, due to the umask and disabling of the commands mentioned above.
~ftp/tmp
This directory is used to create temporary files which contain the error messages generated by a conversion or
LIST command. The owner should be the user “ftp”. The permissions should be 300.
If you don't enable conversion commands, or don't want anonymous users uploading files here (see
~ftp/incoming above), then don't create this directory. However, error messages from conversion or
LIST commands won't be returned to the user. (This is the traditional behaviour.) Note that the
ftpd.conf(5) directive
upload can be used to prevent users uploading here.
To set up "ftp-only" accounts that provide only FTP, but no valid shell login, you can copy/link
/sbin/nologin to
/sbin/ftplogin, and enter
/sbin/ftplogin to
/etc/shells to allow logging-in via FTP into the accounts, which must have
/sbin/ftplogin as login shell.