ftpd(1M) (man pages section 1M: System Administration Commands)

man pages section 1M: System Administration Commands

ftpd(1M)

NAME

in.ftpd, ftpd– file transfer protocol server

SYNOPSIS

in.ftpd

-dl

-t

timeout

DESCRIPTION

in.ftpd is the Internet File Transfer Protocol ( FTP ) server process. The server is invoked by the Internet daemon inetd(1M) each time a connection to the FTP service (see services(4)) is made.

OPTIONS

-d: Debugging information is logged to the system log daemon syslogd(1M).
-l: Each FTP session is logged to the system log daemon syslogd(1M).
-t timeout: Set the inactivity timeout period to timeout seconds. The FTP server will timeout an inactive session after 15 minutes.

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
EPSV: extended passive command request
LPSV: long passive command request
PORT: specify data connection port
EPRT: specify extended address for the transport connection
LPRT: specify “long” address for the transport connection
PWD: print the current working directory
QUIT: terminate session
RETR: retrieve a file
RMD: remove a directory
RNFR: specify rename-from file name
RNTO: specify rename-to file name
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 remaining FTP requests specified in RFC 959 are recognized, but not implemented.

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.in.ftpd interprets file names according to the “globbing” conventions used by sh(1). This allows users to utilize the metacharacters: * ? [ ] { } ~ in.ftpd's umask (which it uses to create files during PUT operations) may be adjusted by adding the line

UMASK=nnn

to /etc/default/ftpd.

The banner returned by in.ftpd in the parenthetical portion of its greeting is configurable. The default is equivalent to "`uname -sr`" and will be used if no banner is set in /etc/default/ftpd. To set the banner, add a line of the form

BANNER="..."

/etc/default/ftpd

The default banner may also be obtained by

BANNER="`uname -s` `uname -r`"

/etc/default/ftpd

BANNER="

in.ftpd authenticates users according to four rules.

First, the user name must be in the password data base, /etc/passwd, and have a password that is not NULL. A password must always be provided by the client before any file operations may be performed. The PAM framework (see SECURITY below) is used to verify that the correct password was entered.

Second, if the user name appears in the file /etc/ftpusers, ftp access is denied. The default list of users in /etc/ftpusers includes all of the accounts in passwd(4). See ftpusers(4).

Third, ftp access is denied if the user's shell is not a shell listed in getusershell(3C).

Fourth, if the user name is “anonymous” or “ftp”, an entry for the user name ftp must be present in the password and shadow files. The user is then allowed to log in by specifying any password — by convention this is given as the user's e-mail address (such as user@host.Sun.COM). Do not specify a valid shell in the password entry of the ftp user, and do not give it a valid password (use NP in the encrypted password field of the shadow file).

For anonymous ftp users, in.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 suggested.

~ftp

Make the home directory owned by root and unwritable by anyone.

~ftp/bin

Make this directory owned by the superuser and unwritable by anyone. Make this a symbolic link to ~ftp/usr/bin The program ls(1) must be present to support the list commands. This program should have mode 111.

~ftp/usr/lib

Make this directory owned by the superuser and unwritable by anyone. Copy the following shared libraries from /usr/lib into this directory:

ld.so.1*
libc.so.1*
libdl.so.1*
libmp.so.2*
libnsl.so.1*
libsocket.so.1*
nss_compat.so.1*
nss_dns.so.1*
nss_files.so.1*
nss_nis.so.1*
nss_nisplus.so.1*
nss_xfn.so.1*
straddr.so*
straddr.so.2*

~ftp/etc

Make this directory owned by the superuser and unwritable by anyone. Copies of the files passwd(4), group(4), and netconfig(4) must be present for the ls(1) command to work properly. These files should be mode 444.

~ftp/pub

Make this directory mode 755 and owned by root. Users should then place files which are to be accessible via the anonymous account in this directory.

~ftp/dev

Make this directory owned by the superuser and unwritable by anyone. First perform ls -lL on the device files listed below to determine their major and minor numbers, then use mknod to create them in this directory.

/dev/zero
/dev/tcp
/dev/udp
/dev/ticotsord

Set the read and write mode on these nodes to 666 so that passive ftp will not fail with “permission denied” errors.

~ftp/usr/share/lib/zoneinfo

Make this directory mode 555 and owned by the superuser. Copy its contents from /usr/share/lib/zoneinfo. This enables ls -l to display time and date stamps correctly.

SECURITY

in.ftpd uses pam(3PAM) for authentication, account management, and session management. The PAM configuration policy, listed through /etc/pam.conf, specifies the module to be used for in.ftpd. Here is a partial pam.conf file with entries for the in.ftpd command using the UNIX authentication, account management, and session management module.

ftp	auth	required	/usr/lib/security/pam_unix.so.1
ftp	account	required	/usr/lib/security/pam_unix.so.1
ftp	session	required	/usr/lib/security/pam_unix.so.1

If there are no entries for the ftp service, then the entries for the "other" service will be used. Unlike login, passwd, and other commands, the ftp protocol will only support a single password. Using multiple modules will prevent in.ftpd from working properly.

USAGE

The in.ftpd command is IPv6–enabled. See ip6(7P).

EXAMPLES

Example 1 Setting Up An Anonymous Ftp

To set up anonymous ftp, add the following entry to the /etc/passwd file. In this example, /export/ftp was chosen to be the anonymous ftp area, and the shell is the non-existent file /nosuchshell. This prevents users from logging in as the ftp user.

ftp:x:30000:30000:Anonymous FTP:/export/ftp:/nosuchshell

Add the following entry to the /etc/shadow file:

ftp:NP:6445::::::

The following shell script sets up the anonymous ftp area. It presumes that names are resolved using NIS.

#!/bin/sh
     # script to setup anonymous ftp area
     #

     # verify you are root
     /usr/bin/id | grep -w 'uid=0' >/dev/null 2>&1
     if [ "$?" != "0" ]; then
        echo
        exit 1
     fi

     # handle the optional command line argument
     case $# in

        # the default location for the anon ftp comes from the passwd file
        0) ftphome="`getent passwd ftp | cut -d: -f6`"
           ;;

        1) if [ "$1" = "start" ]; then
              ftphome="`getent passwd ftp | cut -d: -f6`"
           else
              ftphome=$1
           fi
           ;;

        *) echo "Usage: $0 [anon-ftp-root]"
           exit 1
           ;;
     esac

     if [ -z "${ftphome}" ]; then
        echo "$0: ftphome must be non-null"
        exit 2
     fi

     case ${ftphome} in
        /*) # ok
            ;;

        *) echo "$0: ftphome must be an absolute pathname"
           exit 1
           ;;
     esac

     # This script assumes that ftphome is neither / nor /usr so ...
     if [ -z "${ftphome}" -o "${ftphome}" = "/" -o "${ftphome}" = "/usr" ]; then
        echo "$0: ftphome must be non-null and neither / or /usr"
        exit 2
     fi

     # If ftphome does not exist but parent does, create ftphome
     if [ ! -d ${ftphome} ]; then
         # lack of -p below is intentional
         mkdir ${ftphome}
     fi
     chown root ${ftphome}
     chmod 555 ${ftphome}

     echo Setting up anonymous ftp area ${ftphome}

     # Ensure that the /usr directory exists
     if [ ! -d ${ftphome}/usr ]; then
         mkdir -p ${ftphome}/usr
     fi
     # Now set the ownership and modes to match the man page
     chown root ${ftphome}/usr
     chmod 555 ${ftphome}/usr

     # Ensure that the /usr/bin directory exists
     if [ ! -d ${ftphome}/usr/bin ]; then
         mkdir -p ${ftphome}/usr/bin
     fi
     # Now set the ownership and modes to match the man page
     chown root ${ftphome}/usr/bin
     chmod 555 ${ftphome}/usr/bin

     # this may not be the right thing to do
     # but we need the bin -> usr/bin link
     rm -f ${ftphome}/bin
     ln -s usr/bin ${ftphome}/bin

     # Ensure that the /usr/lib and /etc directories exist
     if [ ! -d ${ftphome}/usr/lib ]; then
         mkdir -p ${ftphome}/usr/lib
     fi
     chown root ${ftphome}/usr/lib
     chmod 555 ${ftphome}/usr/lib

     if [ ! -d ${ftphome}/usr/lib/security ]; then
         mkdir -p ${ftphome}/usr/lib/security
     fi
     chown root ${ftphome}/usr/lib/security
     chmod 555 ${ftphome}/usr/lib/security

     if [ ! -d ${ftphome}/etc ]; then
         mkdir -p ${ftphome}/etc
     fi
     chown root ${ftphome}/etc
     chmod 555 ${ftphome}/etc


     # a list of all the commands that should be copied to ${ftphome}/usr/bin
     # /usr/bin/ls is needed at a minimum.
     ftpcmd="
        /usr/bin/ls
     "

     # ${ftphome}/usr/lib needs to have all the libraries needed by the above
     # commands, plus the runtime linker, and some name service libraries

     # to resolve names. We just take all of them here.

     ftplib="`ldd $ftpcmd | nawk '$3 ~ /lib/ { print $3 }' | sort | uniq`"
     ftplib="$ftplib /usr/lib/nss_* /usr/lib/straddr* /usr/lib/libmp.so*"
     ftplib="$ftplib /usr/lib/libnsl.so.1 /usr/lib/libsocket.so.1 /usr/lib/ld.so.1"
     ftplib="`echo $ftplib | tr ' ' '\n' | sort | uniq`"

     cp ${ftplib} ${ftphome}/usr/lib
     chmod 555 ${ftphome}/usr/lib/*

     cp /usr/lib/security/* ${ftphome}/usr/lib/security
     chmod 555 ${ftphome}/usr/lib/security/*

     cp ${ftpcmd} ${ftphome}/usr/bin
     chmod 111 ${ftphome}/usr/bin/*

     # you also might want to have separate minimal versions of passwd and group
     cp /etc/passwd /etc/group /etc/netconfig /etc/pam.conf ${ftphome}/etc
     chmod 444 ${ftphome}/etc/*

     # need /etc/default/init for timezone to be correct
     if [ ! -d ${ftphome}/etc/default ]; then
        mkdir ${ftphome}/etc/default
     fi
     chown root ${ftphome}/etc/default
     chmod 555 ${ftphome}/etc/default
     cp /etc/default/init ${ftphome}/etc/default
     chmod 444 ${ftphome}/etc/default/init

     # Copy timezone database
     mkdir -p ${ftphome}/usr/share/lib/zoneinfo
     (cd ${ftphome}/usr/share/lib/zoneinfo
       (cd /usr/share/lib/zoneinfo; find . -print |
        cpio -o) 2>/dev/null | cpio -imdu 2>/dev/null
       find . -print | xargs chmod 555
       find . -print | xargs chown root
     )

     # Ensure that the /dev directory exists
     if [ ! -d ${ftphome}/dev ]; then
         mkdir -p ${ftphome}/dev
     fi

     # make device nodes. ticotsord and udp are necessary for
     # 'ls' to resolve NIS names.

     for device in zero tcp udp ticotsord ticlts
     do
        line=`ls -lL /dev/${device} | sed -e 's/,//'`
        major=`echo $line | awk '{print $5}'`
        minor=`echo $line | awk '{print $6}'`
        rm -f ${ftphome}/dev/${device}
        mknod ${ftphome}/dev/${device} c ${major} ${minor}
     done

    chmod 666 ${ftphome}/dev/*

     ## Now set the ownership and modes
     chown root ${ftphome}/dev
     chmod 555 ${ftphome}/dev

     # uncomment the below if you want a place for people to store things,
     # but beware the security implications
     #if [ ! -d ${ftphome}/pub ]; then
     #   mkdir -p ${ftphome}/pub
     #fi
     #chown root ${ftphome}/pub
     #chmod 1755 ${ftphome}/pub

~ftp/etc

ATTRIBUTES

See attributes (5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Availability	SUNWcsu

FILES

/etc/default/ftpd
/etc/ftpusers: file listing users for whom ftp login privileges are disallowed.

DIAGNOSTICS

in.ftpd logs various errors to syslogd, with a facility code of daemon.

Info Severity

These messages are logged only if the -l flag is specified.

FTPD: connection from host at time: A connection was made to ftpd from the host host at the date and time time.
FTPD: User user timed out after timeout seconds at time: The user user was logged out because they had not entered any commands after timeout seconds; the logout occurred at the date and time time.

Debug Severity

These messages are logged only if the -d flag is specified.

FTPD: command: command: A command line containing command was read from the FTP client.
lost connection: The FTP client dropped the connection.
<--- replycode <--- replycode-: A reply was sent to the FTP client with the reply code replycode. The next message logged will include the message associated with the reply. If a - follows the reply code, the reply is continued on later lines.

NOTES

The anonymous ftp account is inherently dangerous and should be avoided when possible.

The name service caching daemon /usr/sbin/nscd may interfere with some of the functionality of anonymous ftp. The sublogin feature does not work unless caching for passwd is disabled in /etc/nscd.conf.

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 possibly incomplete.

The file /etc/ftpusers, which is now included as part of Solaris, contains a list of users who cannot access the system; the default list of users in /etc/ftpusers includes all of the accounts in passwd(4). See ftpusers(4).

SunOS 5.8 Last Revised 8 Dec 1999