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FTPD(8) BSD System Manager's Manual FTPD(8) NAME ftpd -- Internet File Transfer Protocol server SYNOPSIS ftpd [-46AdDEmMoOrRSUvW] [-l [-l]] [-a address] [-p file] [-t timeout] [-T maxtimeout] [-u umask] DESCRIPTION Ftpd is the 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(5). Available options: -4 When -D is specified, accept IPv4 connections. When -6 is also specified, accept IPv4 connection via AF_INET6 socket. When -6 is not specified, accept IPv4 connection via AF_INET socket. -6 When -D is specified, accept connections via AF_INET6 socket. -a When -D is specified, accept connections only on the specified address. -A Allow only anonymous ftp access. -d Debugging information is written to the syslog using LOG_FTP. -D With this option set, ftpd will detach and become a daemon, ac- cepting connections on the FTP port and forking children pro- cesses to handle them. This is lower overhead than starting ftpd from inetd(8) and is thus useful on busy servers to reduce load. -E Disable the EPSV command. This is useful for servers behind older firewalls. -l Each successful and failed ftp(1) session is logged using syslog with a facility of LOG_FTP. If this option is specified twice, the retrieve (get), store (put), append, delete, make directory, remove directory and rename operations and their filename argu- ments are also logged. Note: LOG_FTP messages are not displayed by syslogd(8) by default, and may have to be enabled in syslogd(8)'s configuration file. -m Permit anonymous users to overwrite or modify existing files if allowed by filesystem permissions. By default, anonymous users cannot modify existing files; in particular, files to upload will be created under a unique name. -M Prevent anonymous users from creating directories. -o Put server in write-only mode. RETR is disabled, preventing downloads. -O Put server in write-only mode for anonymous users only. RETR is disabled for anonymous users, preventing anonymous downloads. This has no effect if -o is also specified. -p When -D is specified, write the daemon's process ID to file. -r Put server in read-only mode. All commands which may modify the local filesystem are disabled. -R With this option set, ftpd will revert to historical behavior with regard to security checks on user operations and restric- tions on PORT requests. Currently, ftpd will only honor PORT commands directed to unprivileged ports on the remote user's host (which violates the FTP protocol specification but closes some security holes). -S With this option set, ftpd logs all anonymous file downloads to the file /var/log/ftpd when this file exists. -t The inactivity timeout period is set to timeout seconds (the de- fault is 15 minutes). -T 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. -u The default file creation mode mask is set to umask, which is ex- pected to be an octal numeric value. Refer to umask(2) for de- tails. -U In previous versions of ftpd, when a passive mode client re- quested a data connection to the server, the server would use data ports in the range 1024..4999. Now, by default, the server will use data ports in the range 49152..65535. Specifying this option will revert to the old behavior. -v A synonym for -d. -W Don't log FTP sessions to /var/log/wtmp. The file /var/run/nologin can be used to disable ftp access. If the file exists, ftpd displays it and exits. If the file /etc/ftpwelcome exists, ftpd prints it before issuing the "ready" message. If the file /etc/ftpmotd exists, ftpd prints it after a successful login. Note the motd file used is the one relative to the login environment. This means the one in ~ftp/etc in the anonymous user's case. The ftp server currently supports the following ftp requests. The case of the requests is ignored. Requests marked [RW] are disabled if -r is specified. Request Description ABOR abort previous command ACCT specify account (ignored) ALLO allocate storage (vacuously) APPE append to a file [RW] CDUP change to parent of current working directory CWD change working directory DELE delete a file [RW] EPRT specify data connection port, multiprotocol EPSV prepare for server-to-server transfer, multiprotocol HELP give help information LIST give list files in a directory ("ls -lgA") LPRT specify data connection port, multiprotocol LPSV prepare for server-to-server transfer, multiprotocol MDTM show last modification time of file MKD make a directory [RW] 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 [RW] RNFR specify rename-from file name [RW] RNTO specify rename-to file name [RW] SITE non-standard commands (see next section) SIZE return size of file STAT return status of server STOR store a file [RW] STOU store a file with a unique name [RW] 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) [RW] XPWD print the current working directory (deprecated) XRMD remove a directory (deprecated) [RW] 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 [RW], e.g. ``SITE CHMOD 755 filename'' MD5 report the files MD5 checksum, e.g. ``SITE MD5 filename'' HELP give help information Note: SITE requests are disabled in case of anonymous logins. 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. To avoid possible denial-of- service attacks, SIZE requests against files larger than 10240 bytes will be denied if the current transfer type is ASCII. The ftp server will abort an active file transfer only when the ABOR com- mand 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 six rules. 1. The login name must be in the password data base and not have a null password. In this case a password must be provided by the client before any file operations may be performed. If the user has an S/Key key, the response from a successful USER command will include an S/Key challenge. The client may choose to respond with a PASS command giving either a standard password or an S/Key one-time password. The server will auto- matically determine which type of password it has been given and attempt to authenticate accordingly. See key(1) for more information on S/Key authentication. S/Key is a Trademark of Bellcore. 2. The login name must not appear in the file /etc/ftpusers. 3. The login name must not be a member of a group specified in the file /etc/ftpusers. Entries in this file interpreted as group names are prefixed by an "at" `@' sign. 4. The user must have a standard shell returned by getusershell(3). 5. If the user name appears in the file /etc/ftpchroot, or the user is a member of a group with a group entry in this file, i.e. one prefixed with `@', the session's root will be changed to the user's login directory by chroot(2) as for an "anonymous" or "ftp" account (see next item). This facility may also be triggered by enabling the boolean "ftp-chroot" ca- pability in login.conf(5). However, the user must still sup- ply a password. This feature is intended as a compromise be- tween a fully anonymous account and a fully privileged ac- count. The account should also be set up as for an anonymous account. 6. If the user name is "anonymous" or "ftp", an anonymous ftp ac- count 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 an email address for the user should be used as the password). When the -S option is set, all transfers are logged as well. In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot(2) 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, following these rules: ~ftp Make the home directory owned by "root" and unwritable by anyone. ~ftp/etc Make this directory owned by "root" and unwritable by anyone (mode 555). The files pwd.db (see passwd(5)) and group(5) must be present for the ls command to be able to produce owner names rather than numbers. The password field in passwd is not used, and should not contain real passwords. The file ftpmotd, if present, will be printed after a successful login. These files should be mode 444. ~ftp/pub This directory and the subdirectories beneath it should be owned by the users and groups responsible for placing files in them, and be writable only by them (mode 755 or 775). They should not be owned or writable by "ftp" or its group, otherwise guest users can fill the drive with unwanted files. If the system has multiple IP addresses, ftpd supports the idea of vir- tual hosts, which provides the ability to define multiple anonymous ftp areas, each one allocated to a different internet address. The file /etc/ftphosts contains information pertaining to each of the virtual hosts. Each host is defined on its own line which contains a number of fields separated by whitespace: hostname Contains the hostname or IP address of the virtual host. user Contains a user record in the system password file. As with normal anonymous ftp, this user's access uid, gid and group memberships determine file access to the anony- mous ftp area. The anonymous ftp area (to which any user is chrooted on login) is determined by the home directory defined for the account. User id and group for any ftp account may be the same as for the standard ftp user. statfile File to which all file transfers are logged, which de- faults to /var/log/ftpd. welcome This file is the welcome message displayed before the server ready prompt. It defaults to /etc/ftpwelcome. motd This file is displayed after the user logs in. It de- faults to /etc/ftpmotd. Lines beginning with a '#' are ignored and can be used to include com- ments. Defining a virtual host for the primary IP address or hostname changes the default for ftp logins to that address. The 'user', 'statfile', 'welcome' and 'motd' fields may be left blank, or a single hypen '-' used to indicate that the default value is to be used. As with any anonymous login configuration, due care must be given to setup and maintenance to guard against security related problems. ftpd has internal support for handling remote requests to list files, and will not execute /bin/ls in either a chrooted or non-chrooted environ- ment. The ~/bin/ls executable need not be placed into the chrooted tree, nor need the ~/bin directory exist. FILES /etc/ftpusers List of unwelcome/restricted users. /etc/ftpchroot List of normal users who should be chroot'd. /etc/ftphosts Virtual hosting configuration file. /etc/ftpwelcome Welcome notice. /etc/ftpmotd Welcome notice after login. /var/run/nologin Displayed and access refused. /var/log/ftpd Log file for anonymous transfers. SEE ALSO ftp(1), key(1), umask(2), getusershell(3), login.conf(5), inetd(8), syslogd(8) BUGS 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 possi- bly incomplete. HISTORY The ftpd command appeared in 4.2BSD. IPv6 support was added in WIDE Hy- drangea IPv6 stack kit. BSD January 27, 2000 BSD
NAME | SYNOPSIS | DESCRIPTION | FILES | SEE ALSO | BUGS | HISTORY
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