ftpd - DARPA Internet File Transfer Protocol server
ftpd [ -d ] [ -v ] [ -l ] [ -ttimeout ] [ -Tmaxtimeout ] [ -a ] [ -A ] [ -L ] [ -i ] [ -o ] -uumask ]
Ftpd is the DARPA 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).
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 syslog.
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.
If the -o option is specified, files transmitted by the ftpd(8) server will be logged to the syslog. The -o option is overridden by the use of the ftpaccess(5) file.
If the -u option is specified, the default umask is set to umask.
The ftp server currently supports the following ftp requests; case is not distinguished.
|
Request |
Description | |
|
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.
|
Request |
Description | |
|
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 returned.
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 performed. | ||
|
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 name). |
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 anyone. |
~ftp/bin)
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.
~ftp/etc)
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.
~ftp/pub)
Create a subdirectory in ~ftp/pub with the appropriate mode (777 or 733) if you want to allow normal users to upload files.
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
transmitting
<filename> <filename>.tar Tar <filename>
before transmitting
<filename> <filename>.tar.Z Tar and compress
<filename> before
transmitting
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 lreply() function.
The FTP server can also log all file transmission and reception, keeping the following information for each file transmission that takes place.
Mon Dec 3 18:52:41 1990 1 wuarchive.wustl.edu 568881 /files.lst.Z a _ o a chris@wugate.wustl.edu 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
user (i>ncoming)
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)
0 none
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 possible.
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 possibly incomplete.