in.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
PORT specify data connection port
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="..."
to /etc/default/ftpd. Nonempty banner strings are fed to shells for evaluation. The default banner may also be obtained by
BANNER="`uname -s` `uname -r`"
and no banner will be printed if /etc/default/ftpd contains
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.
Third, ftp access is denied if the user’s shell (from /etc/passwd) is not listed in the file /etc/shells. If the file /etc/shells does not exist, then the user’s shell must be one of the following:
| /usr/bin/sh | /usr/bin/csh | /usr/bin/ksh |
| /usr/bin/jsh | /bin/sh | /bin/csh |
| /bin/ksh | /bin/jsh | /sbin/sh |
| /sbin/jsh |
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. This directory should not be on a file system mounted with the nosuid option.
~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 777 and owned by ftp. 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(3) 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.
EXAMPLES
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}/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 ’ ’ ’0 | sort | uniq‘"
cp ${ftplib} ${ftphome}/usr/lib
chmod 555 ${ftphome}/usr/lib/∗
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 ${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 ftp ${ftphome}/pub
#chmod 1777 ${ftphome}/pub
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Availability | SUNWcsu |
FILES
/etc/default/ftpd
SEE ALSO
ftp(1), ld.so.1.1(1), ls(1), sh(1), aset(1M), inetd(1M), mknod(1M), syslogd(1M), chroot(2), getsockopt(3N), pam(3), group(4), inetd.conf(4), netconfig(4), netrc(4), pam.conf(4), passwd(4), services(4), attributes(5), pam_unix(5)
Postel, Jon, and Joyce Reynolds, File Transfer Protocol ( FTP ), RFC 959, Network Information Center, SRI International, Menlo Park, Calif., October 1985.
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.
/etc/ftpusers contains a list of users who cannot access the system; the format of the file is one user name per line.
SunOS 5.6 — Last change: 4 Mar 1997