ftpd(8)ftpd(8)NAMEftpd - The File Transfer Protocol server daemon, including anonymous
service
SYNOPSISftpd [-dlnxK] [-t time-out] [-T maxtime-out]
OPTIONS
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)). Disables
reverse lookups of remote host names. This option can prevent login
delays and timeouts in an environment where host name resolution is
sluggish. The inactivity time-out period will be set to time-out sec‐
onds. The maximum time-out period allowed may be set to time-out sec‐
onds 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 connec‐
tions 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 connec‐
tions 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 connec‐
tions 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 ser‐
vice 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 connec‐
tion 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 user name must be in the password data‐
base, /etc/passwd, and not have a null password. In this case, a pass‐
word must be provided by the client before any file operations may be
performed. The user name 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 user name is anonymous or ftp, an anony‐
mous 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 authen‐
ticate the client, server, and user, encrypt data, and ensure data
integrity and nonrepudiation. See your system administrator to deter‐
mine 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 Ker‐
beros Ticket Granting Ticket (TGT). Users with a valid TGT are not
prompted for a user name 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 recog‐
nized, 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: Low delay High throughput
Anonymous FTP Configuration
If you are creating an anonymous FTP account, ftpd takes special mea‐
sures 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 direc‐
tories 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).
FILES
Specifies the command path. Contains the list of unauthorized users.
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 pos‐
sibly incomplete.
SEE ALSO
Commands: ftp(1), syslogd(8)
Functions: getusershell(3)
Files: iptos(4)
Guides: Security Administration
ftpd(8)