ftpd(1M) ftpd(1M)
NAME
ftpd - Internet file transfer protocol server
SYNOPSIS
in.ftpd [-dlv] [-u mask] [-t timeout] [-T maxtimeout]
DESCRIPTION
The ftpd command 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 name specification
[see services(4)].
Files
/etc/ftpusers restricted user list
/etc/shells allowed shell list
/etc/passwd the user database
/etc/group the group database
USAGE
ftpd is started by the ``super-server'' inetd, and therefore
must have an entry in inetd's configuration file,
/etc/inetd.conf [see inetd(1M) and inetd.conf(4)].
Options
ftpd takes the following options:
-d Enable debugging. Debugging information is written to
the syslog.
-l Log each FTP session to the syslog.
-v Enables debugging in verbose mode.
-u mask
Set the file creation mask to mask.
-t timeout
Set the inactivity timeout period to timeout seconds.
By default, the FTP server will timeout an inactive
session after 15 minutes.
-T maxtimeout
Limit the maximum timeout period which can be requested
by a client to maxtimeout seconds. The default limit is
2 hours.
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ftpd(1M) ftpd(1M)
FTP Requests
The FTP server currently supports the following FTP requests;
case is not distinguished.
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 -lg)
MKD make a directory
MODE specify data transfer mode
NLST give name list of files in directory (ls)
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 a file 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
TYPE specify data transfer type
USER specify user name
XCUP change to parent of current working directory
XCWD change working directory
XMKD make a directory
XPWD print the current working directory
XRMD remove a directory
The following non-standard or UNIX-specific commands are
supported by the SITE request.
UMASK change umask, for example, SITE UMASK 002
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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 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 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 sh(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, and not have a null password. 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.
This file is checked on each non-anonymous ftp connection
request. If the requested user name is located in the
file, the request is denied. It is suggested that this
file contain at least the following names: uucp, root.
3. The FTP server will not allow FTP logins to accounts whose
shell is not listed in /etc/shells. This typically
restricts access by UUCP sign-ons, etc.
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.
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ftpd(1M) ftpd(1M)
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.
home_directory
Make the home directory owned by ftp and unwritable by
anyone.
home_directory/bin
Make this directory owned by a privileged user and
unwritable by anyone. The program ls(1) must be
present to support the list commands. This program
should have mode 111.
home_directory/usr/lib
Make this directory owned by a privileged user and
unwritable by anyone. The libraries libc.so.1 and
libc.so.1.1 must be present to support the list
commands (they can be copied from your system's
/usr/lib). These files should have mode 111.
home_directory/etc
Make this directory owned by a privileged user and
unwritable by anyone. Copies of the files passwd(4),
group(4), and netconfig must be present for the ls
command to work properly. These files should be mode
444.
home_directory/pub
Make this directory mode 777 and owned by ftp. Users
should then place files which are to be accessible via
the anonymous account in this directory.
home_directory/dev
Make this directory owned by a privileged user and
unwritable by anyone. Change directories to this
directory and do the following:
FTP="`grep ^ftp: /etc/passwd | cut -d: -f6`"
MAJORMINOR="`ls -l /dev/tcp | nawk '{ gsub(/,/, ""); print $5, $6}'`
mknod $FTP/dev/tcp c $MAJORMINOR
chmod 666 $FTP/dev/tcp
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ftpd(1M) ftpd(1M)
General Considerations
/etc/ftpusers contains a list of users who cannot access the
system; the format of the file is one username per line.
If a remote user does not have a home directory, the root
directory (/) becomes the user's current directory.
Warnings
The anonymous account is inherently dangerous and should be
avoided when possible.
The server must run as a privileged process to create sockets
with privileged port numbers. It maintains an effective user
ID of the logged-in user, changing to user ID 0 only when
binding addresses to sockets. The possible security holes
have been extensively scrutinized, but are possibly
incomplete.
REFERENCES
ftp(1), getsockopt(3N), passwd(4), services(4), syslog(3G)
RFC 959
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