ftpd - The File Transfer Protocol server daemon, including
anonymous service
ftpd [-dlxK] [-t timeout] [-T maxtimeout]
Debugging information is sent to the syslogd daemon (see
syslogd(8)). 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)). The inactivity
time-out period will be set to time-out seconds.
The maximum timeout period allowed may be set to timeout
seconds with this option. 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. 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.
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.
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
The ftp command uses the default Type-of-Service values
recommended by RFC1060, which are as follows: Low delay
High throughput
Anonymous FTP Configuration [Toc] [Back]
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: Make
the home directory owned by the superuser (root) and
unwritable by anyone. 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. 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. 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).
Specifies the command path. Contains the list of unauthorized
users. Specifies the path name for the banner file.
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.
Commands: ftp(1), syslogd(8)
Functions: getusershell(3)
Files: iptos(4)
Guides: Security Administration
ftpd(8)
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