ftpd - Internet File Transfer Protocol server
ftpd [ -d ] [ -v ] [ -l ] [ -t timeout ] [ -T maxtimeout ] [ -a ] [ -A
] [ -L ] [ -i ] [ -I ] [ -o ] [ -p ctrlport ] [ -P dataport ] [ -q ] [
-Q ] [ -r rootdir ] [ -R ] [ -s ] [ -S ] [ -u umask ] [ -V ] [ -w ] [
-W ] [ -X ]
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).
The -V option causes the program to display copyright and version
information, then terminate.
If the -d or -v option is specified, debugging information is written
to the syslog.
If the -l option is specified, each ftp session is logged in the
The ftp server will timeout an inactive session after 15 minutes. If
the -t option is specified, the inactivity timeout period will be set
to timeout seconds. 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.
If the -a option is specified, the use of the ftpaccess(5)
configuration file is enabled.
If the -A option is specified, use of the ftpaccess(5) configuration
file is disabled. This is the default.
If the -L option is specified, commands sent to the ftpd(8) server will
be logged to the syslog. The -L option is overridden by the use of the
ftpaccess(5) file. If the -L flag is used, command logging will be on
by default as soon as the ftp server is invoked. This will cause the
server to log all USER commands, which if a user accidentally enters a
password for that command instead of the username, will cause passwords
to be logged via syslog.
If the -i option is specified, files received by the ftpd(8) server
will be logged to the xferlog(5). The -i option is overridden by the
use of the ftpaccess(5) file.
The -I option disables the use of RFC931 (AUTH/ident) to attempt to
determine the username on the client.
If the -o option is specified, files transmitted by the ftpd(8) server
will be logged to the xferlog(5). The -o option is overridden by the
use of the ftpaccess(5) file. If the -X option is specified, the
output created by the -i and -o options is not saved to the xferlog
file but saved via syslog so you can collect output from several hosts
on one central loghost.
If the -u option is specified, the default umask is set to umask.
If the -W option is specified user logins are not recorded in the wtmp
file. The default ( -w ) is to record every login and logout.
The -s and -S options place the daemon in standalone operation mode.
The -S option runs the daemon in the background and is useful in
startup scripts during system initialization (ie., in rc.local). The
-s option leaves the daemon in foreground and is useful when running
from init (ie., /etc/inittab).
The -p and -P options override the port numbers used by the daemon.
Normally, the daemon determines the port numbers by looking in
/etc/services for "ftp" and "ftp-data". If there is no /etc/services
entry for "ftp-data" and the -P option is not specified, the daemon
uses the port just prior to the control connection port. The -p option
is only available if running as a standalone daemon.
The -q and -Q options deterine whether the daemon uses the PID files.
These files are required by the limit directive to determine the number
of current users in each access class. Disabling the use of the PID
files disables user limits. The default ( -q ) is to use the PID
files. Specify -Q when testing the server as a normal user when access
permissions prevent the use of the PID files. Large, busy sites which
do not wish to impose limits on the number of concurrent users may also
consider disabling the PID files.
The -r option instructs the daemon to chroot(2) to the specified
rootdir immedeately upon loading. This can improve system security by
limiting the files which may be damaged should a breakin occur through
the daemon. Set is much like anonymous FTP, with additional files
needed which vary from system to system.
When started with -R the daemon will not honour the REST command,
possibly preventing "download managers" from hogging your bandwidth.
The ftp server currently supports the following ftp requests; case is
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
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.
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. E.g. SITE HELP
NEWER list files newer than a particular date
MINFO like SITE NEWER, but gives extra information
GROUP request special group access. E.g. SITE GROUP foo
GPASS give special group access password. E.g. SITE GPASS bar
EXEC execute a program. E.g. SITE EXEC program params
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
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 four rules.
1) The user name must be in the password data base, /etc/passwd, or
whatever is appropriate for the operating system, and the
password must not be null. In this case a password must be
provided by the client before any file operations may be
2) The user name must not appear in the file /etc/ftpusers.
3) The user must have a standard shell returned by getusershell(3).
4) 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 this is given as the client host’s
In the last case, ftpd takes special measures to restrict the client’s
access privileges. The server performs a chroot(2) command 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; the following rules are recommended.
~ftp) Make the home directory owned by super-user and unwritable by
Make this directory owned by the super-user and unwritable by
anyone. The program ls(1) must be present to support the list
command. This program should have mode 111.
Make this directory owned by the super-user and unwritable by
anyone. The files passwd(5) and group(5) must be present for
the ls command to be able to produce owner names rather than
numbers. Depending on the operating system, there may be other
required files. Check your manual page for the getpwent(3)
library routine. The password field in passwd is not used, and
should not contain real encrypted passwords. These files should
be mode 444 and owned by the super-user. Don’t use the system’s
/etc/passwd file as the password file or the system’s /etc/group
file as the group file in the ~ftp/etc directory.
Create a subdirectory in ~ftp/pub with the appropriate mode (777
or 733) if you want to allow normal users to upload files.
AUTHENTICATION MECHANISM ON BSD/OS SYSTEMS ONLY
The authentication mechanism used by ftpd is determined by the ‘‘auth-
ftp’’ entry in the /etc/login.conf file (see login.conf(5)) that
matches the users class. If there is no ‘‘auth-ftp’’ entry for the
class, the normal ‘‘auth’’ entry will be used instead. An alternate
authentication mechanism may be specified by appending a colon (‘‘:’’)
followed by the authentication style, i.e. ‘‘joe:skey’’.
GENERAL FTP EXTENSIONS
There are some extensions to the FTP server such that if the user
specifies a filename (when using a RETRIEVE command) such that:
True Filename Specified Filename Action
------------- ------------------ -----------------------------------
<filename>.Z <filename> Decompress file before transmitting
<filename> <filename>.Z Compress <filename> before
<filename> <filename>.tar Tar <filename> before transmitting
<filename> <filename>.tar.Z Tar and compress <filename> before
Also, the FTP server will attempt to check for valid e-mail addresses
and chide the user if he doesn’t pass the test. For users whose FTP
client will hang on "long replies" (i.e. multiline responses), using a
dash as the first character of the password will disable the server’s
The FTP server can also log all file transmission and reception,
keeping the following information for each file transmission that takes
Mon Dec 3 18:52:41 1990 1 wuarchive.wustl.edu 568881 /files.lst.Z a _ o a email@example.com ftp 0 *
%.24s %d %s %d %s %c %s %c %c %s %s %d %s
1 2 3 4 5 6 7 8 9 10 11 12 13
1 current time in the form DDD MMM dd hh:mm:ss YYYY
2 transfer time in seconds
3 remote host name
4 file size in bytes
5 name of file
6 transfer type (a>scii, b>inary)
7 special action flags (concatenated as needed):
C file was compressed
U file was uncompressed
T file was tar’ed
_ no action taken
8 file was sent to user (o>utgoing) or received from
9 accessed anonymously (r>eal, a>nonymous, g>uest) -- mostly for FTP
10 local username or, if guest, ID string given
(anonymous FTP password)
11 service name (’ftp’, other)
12 authentication method (bitmask)
1 RFC931 Authentication
13 authenticated user id (if available, ’*’ otherwise)
ftp(1), getusershell(3), syslogd(8), ftpaccess(5), xferlog(5), umask(2)
The anonymous account is inherently dangerous and should avoided when
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