REXECD(1M) REXECD(1M)
rexecd - remote execution server
/usr/etc/rexecd [ -l ]
Rexecd is the server for the rexec(3N) routine. The server provides
remote execution facilities with authentication based on user names and
passwords. NOTE: password aging is not supported by this daemon.
Rexecd listens for service requests at the port indicated in the ``exec''
service specification; see services(4). When a service request is
received the following protocol is initiated:
1) The server reads characters from the socket up to a null (`\0')
byte. The resultant string is interpreted as an ASCII number, base
10.
2) If the number received in step 1 is non-zero, it is interpreted as
the port number of a secondary stream to be used for the stderr. A
second connection is then created to the specified port on the
client's machine.
3) A null-terminated user name of at most 16 characters is retrieved on
the initial socket.
4) A null-terminated, unencrypted password of at most 16 characters is
retrieved on the initial socket.
5) A null-terminated command to be passed to a shell is retrieved on
the initial socket. The length of the command is limited by the
upper bound on the size of the system's argument list.
6) Rexecd then validates the user as is done at login time and, if the
authentication was successful, changes to the user's home directory,
and establishes the user and group protections of the user. If any
of these steps fail the connection is aborted with a diagnostic
message returned.
7) A null byte is returned on the initial socket and the command line
is passed to the normal login shell of the user. The shell inherits
the network connections established by rexecd.
If the Share II system is installed and enabled, then the following
privilege and resource checks are made immediately after validation
checks are complete (rshd(1)) but before the shell is started:
1. If your nologin flag is set, or you already have another connection
and your onelogin flag is set, then you are denied connection.
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2. If a disk usage exceeds the soft disk limit in any of your domains,
then a message is printed and you are given a warning. If you
accumulate too many warnings, further connection attempts are denied
and you must see your subadministrator to rectify the situation.
Whenever you connect with no disk usages in excess of any soft
limits, all your accumulated warnings are cleared.
3. If you do not have permission to use an rexec connection, as
determined by the terminal permission flag terminal.flag.rexec, then
you are denied connection.
4. Some installations place limits on terminal connect-time, which apply
equally to connection by way of rexec. If you have already reached
your connect-time limit, then you are denied connection. Otherwise,
if you have a limit, your remaining connect-time is printed.
If all these checks are passed, rexecd proceeds normally.
For each new instance of a remotely initiated process, rexecd first reads
the configuration file /etc/default/rexecd. Currently the only switch in
this file is SVR4_SIGNALS, which indicates if SVR4 signal defaults should
be used, and defaults to `YES'. This means that processes spawned by
rexecd will run with the SIGXFSZ and SIGXCPU signals disabled (i.e.
ignored). For CPU and filesize resource limiting to work correctly, this
file should be edited and SVR4_SIGNALS set to `NO', so that these signal
retain their default behaviour, which is to terminate the process.
-l This option causes all successful accesses to be logged to
syslogd(1M) as auth.info messages.
/etc/limconf The compiled Share II configuration file (machine
readable).
/etc/default/rexecd Default behaviour configuration file
login(1), rshd(1M), rexec(3N), passwd(4), share(5)
Except for the last one listed below, all diagnostic messages are
returned on the initial socket, after which any network connections are
closed. An error is indicated by a leading byte with a value of 1 (0 is
returned in step 7 above upon successful completion of all the steps
prior to the command execution).
``username too long''
The name is longer than 16 characters.
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``password too long''
The password is longer than 16 characters.
``command too long ''
The command line passed exceeds the size of the argument list (as
configured into the system).
``Login incorrect.''
No password file entry for the user name existed. (Also logged to the
syslogd(1M) daemon as an auth.notice message.)
``Password incorrect.''
The wrong was password supplied. (Also logged to the syslogd(1M) daemon
as an auth.notice message.)
``No remote directory.''
The chdir command to the home directory failed.
``Try again.''
A fork by the server failed.
``<shellname>: ...''
The user's login shell could not be started. This message is returned on
the connection associated with the stderr, and is not preceded by a flag
byte.
The Share II specific diagnostic messages are listed as follows:
``Warning <X> of <Y>: soft disk limit exceeded.''
One of your domains has a disk usage in excess of its soft limit.
``Connection denied. Too many warnings.''
You have reached your warning limit. See your subadministrator.
``Connection denied. Already logged in - only one login allowed.''
You are already connected to the system and your onelogin flag is set.
``Connection denied. Currently barred from logging in.''
Your nologin flag is set.
``Connection denied. No permission to use this terminal.''
You are not allowed to log in at this terminal because of a clear
terminal.flag.rexec flag.
``You have a remaining terminal connect-time of <Y>.''
You may use this connection until you have used up your remaining
connect-time, at which point you are forced to disconnect.
``Connection denied. Terminal connect-time limit exceeded.''
You have already reached your terminal connect-time limit.
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``Share not configured - no limit checks.''
The configuration file is unreadable for some reason, so terminal
privileges, connect-time limits and disk space limits could not be
checked.
Indicating ``Login incorrect'' as opposed to ``Password incorrect'' is a
security breach which allows people to probe a system for users with null
passwords.
A facility to allow all data and password exchanges to be encrypted
should be present.
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