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ftpd(8)
NAME
ftpd - The File Transfer Protocol server daemon, including anonymous
service
SYNOPSIS
ftpd [-dlxK] [-t timeout] [-T maxtimeout]
OPTIONS
-d Debugging information is sent to the syslogd daemon (see syslogd(8)).
-l Each FTP session, as well as additional information, such as the file
name retrieved or stored, the number of bytes, and the attempted logins
that failed, is sent to the syslogd daemon (see syslogd(8)).
-t time-out
The inactivity time-out period will be set to time-out seconds.
-T maxtime-out
The maximum timeout period allowed may be set to timeout seconds with
this option.
-x Encrypts the data transmitted between the local host and the remote
host. This option requires that the local and remote hosts be
configured to use Kerberos authentication in the same or trusting
Kerberos realms.
If the ftpd daemon is started with the -x option, only connections
initiated with the -x option from a remote host will be accepted. All
communications between the two hosts will be encrypted.
-K Specifies that only Kerberos authenticated connections will be
accepted. This option requires that the local and remote hosts be
configured to use Kerberos authentication in the same or trusting
Kerberos realms.
If the ftpd daemon is started with the -K option, only connections
initiated from a host in the same or trusting Kerberos domain will be
accepted. All communications between the two hosts will be encrypted.
SECURITY NOTE
This security-sensitive command uses the SIA (Security Integration
Architecture) routine as an interface to the security mechanisms. See
matrix.conf(4) for more information.
DESCRIPTION
The ftpd command is the DARPA (Defense Advanced Research Projects Agency)
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(4).
The FTP server will time out an inactive session after 15 minutes. If the
-t option is specified, the inactivity time-out period will be set to
time-out seconds. A client may also request a different time-out period;
the maximum period allowed may be set to time-out seconds with the -T
option. The default limit is 2 hours.
If you want to use a customized banner, create an /etc/banner file. The
ftpd daemon reads the file, if it exists, and writes its contents over a
new FTP connection prior to starting the login dialog.
The ftpd command interprets file names according to the ``globbing''
conventions used by the C shell (see csh(1)). This interpretation allows
users to utilize the metacharacters ``*?[]{}~''.
The way in which the ftpd daemon authenticates a user and transmits data
depends on if the local and remote hosts are using a basic connection or a
secure connection (Kerberos). Basic and secure connections provide user
authentication; however, a secure connection also provides client and
server authentication, data encryption, data integrity, and nonrepudiation.
Basic Connection
A basic connection is one where the ftpd daemon authenticates users
according to four rules:
· The username must be in the password database, /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.
· The username must not appear in the /etc/ftpusers file.
· The user must have a standard shell returned by the getusershell()
call (see getusershell(3)).
· If the username is anonymous or ftp, an anonymous ftp account must be
present in the /etc/passwd file (user ftp). In this case, the user is
allowed to log in by specifying any password (by convention this is
given as the client host's name).
Secure Connection
A secure connection is one where the ftpd daemon authenticates a user by
using Kerberos. Kerberos is a client/server application that authenticate
the client, server, and user, encrypt data, and ensure data integrity and
nonrepudiation. See your system administrator to determine if your system
is running Kerberos. See Security Administration for more information about
Kerberos.
Kerberos authenticates by using secret-key cryptography and tickets between
Kerberos clients and Kerberos server in the same or trusting Kerberos
realms. Once authenticated by Kerberos, users receive a Kerberos Ticket
Granting Ticket (TGT). Users with a valid TGT are not prompted for a
username or password when the remote host is in the same or trusting
Kerberos realm.
FTP REQUESTS
The FTP server currently supports the following ftp requests; case is not
distinguished:
________________________________________________________________________
Request Description
________________________________________________________________________
ABOR
Abort previous command.
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.
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.
EPSV
Prepare for proxy transfer (default) and server-to-server
transfer.
EPRT Specify data connection port.
HELP Give help information.
LIST Give list files in a directory (ls -lgA).
LPRT Specify data connection port (IPv6 addresses only).
LPSV Prepare for server-to-server transfer (IPv6 addresses only).
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 (IPv4 addresses only).
PORT Specify data connection port (IPv4 addresses only).
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 Nonstandard commands (see next section)
SIZE Return size of file
STAT
Return status of server. If a STAT command is received during
a data transfer, preceded by a Telnet IP and Synch, transfer
status will be returned.
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 username
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 nonstandard or UNIX compatible commands are supported by the
SITE request:
____________________________________________________________
Request Description
____________________________________________________________
UMASK
Change umask (for example, SITE UMASK 002)
IDLE
Set idle timer (for example, SITE IDLE 60)
CHMOD
Change mode of a file (for example,
SITE CHMOD 755 filename)
HELP
Give help information (for example, SITE HELP)
____________________________________________________________
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.
TYPE-OF-SERVICE VALUES
The ftp command uses the default Type-of-Service values recommended by
RFC1060, which are as follows:
ftp-control
Low delay
ftp-data
High throughput
Anonymous FTP Configuration
If you are creating an anonymous FTP account, ftpd takes special measures
to restrict the client's access privileges when the user logs in. The
server executes a chroot call (see chroot(2)) to the home directory of the
ftp user. In order that system security is not breached, it is recommended
that you adhere to the following rules when creating directories and files
in the ftp subtree:
~ftp
Make the home directory owned by the superuser (root) and unwritable by
anyone.
~ftp/bin
Make this directory owned by the superuser and unwritable by anyone.
The ls program (see ls(1)) must be present to support the list command.
This program should have mode 111.
Copy the ls program from /sbin/ls. This is the statically linked
version of the ls command, which does not require shared library
support. Be sure to copy the static version of ls from the /sbin
directory, not the shared version from the /usr/bin directory.
~ftp/etc
Make this directory owned by the superuser and unwritable by anyone.
The passwd and group files (see passwd(4) and group(4) ) must be
present for the ls command to be able to produce owner names rather
than numbers. The password field in the passwd file is not used, and
should not contain real encrypted passwords. These files should be
mode 444.
In this environment, the sia subdirectory (which you can copy from
/etc/sia) must also be present for the ls command to be able to produce
owner names rather than numbers.
~ftp/pub
Make this directory mode 777 and owned by ftp. Users should then place
files that are to be accessible via the anonymous account in this
directory.
You can configure these values by specifying them in the /etc/iptos file.
For more information, see iptos(4).
FILES
/usr/sbin/ftpd
Specifies the command path.
/etc/ftpusers
Contains the list of unauthorized users.
/etc/banner
Specifies the path name for the banner file.
CAUTIONS
The anonymous account is inherently dangerous and should be avoided when
possible.
The server must run as the superuser to create sockets with privileged port
numbers. It maintains an effective user ID of the logged in user,
reverting to the superuser only when binding addresses to sockets. The
possible security holes have been extensively scrutinized, but are possibly
incomplete.
SEE ALSO
Commands: ftp(1), syslogd(8)
Functions: getusershell(3)
Files: iptos(4)
Guides: Security Administration
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Index for
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Alphabetical
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