conserver(8)
NAME
conserver - console server daemon
SYNOPSIS
conserver [-7dDEFhinoRSuvV] [-a type] [-m max] [-M master] [-p port]
[-b port] [-c cred] [-C config] [-P passwd] [-L logfile] [-O min] [-U
logfile]
DESCRIPTION
Conserver is the daemon that manages remote access to system consoles
by multiple users via the console(1) client program and (optionally)
log the console output. It can connect to consoles via local serial
ports, Unix domain sockets, TCP sockets (for terminal servers and the
like), or any external program.
When started, conserver reads the conserver.cf(5) file for details of each console. The console type, logging options, serial or network parameters, and user access levels are just a few of the things that can be specified. Command-line options are then applied, possibly overriding conserver.cf(5) settings. Conserver categorizes consoles into two types: those it should actively manage, and those it should just know about, so it can refer clients to other conserver instances. If the master value of a console matches the hostname or ip address of the local machine, conserver will actively manage the console. Otherwise, it's considered a ``remote'' console and managed by a different server. Conserver forks a child for each group of consoles it must manage and assigns each process a port number to listen on. The maximum number of consoles managed by each child process is set using the -m option. The console(1) client program communicates with the master console server process to find the port (and host, in a multi-server configuration) on which the appropriate child is listening. Conserver restricts connections from clients based on the host access section of its conserver.cf(5) file, restricts users based on the console access lists of the conserver.cf(5) file, and authenticates users against its conserver.passwd(5) file. Conserver can also restrict clients using the tcp-wrappers package (enabled using --with-libwrap). This authentication is done before consulting the conserver.cf(5) access list.
When Unix domain sockets are used between the client and server
(enabled using --with-uds), authentication checks are done on the hardcoded address ``127.0.0.1''. Automatic client redirection is also disabled (as if the -R option was used) since the client cannot communicate with remote servers. The directory used to hold the sockets is
checked to make sure it's empty when the server starts. The server
will not remove any files in the directory itself, just in case the
directory is accidentally specified as ``/etc'' or some other critical
location. The server will do its best to remove all the sockets when
it shuts down, but it could stop ungracefully (crash, ``kill -9'', etc)
and leave files behind. It would then be up to the admin (or a creative startup script) to clean up the directory before the server will
start again.
Conserver completely controls any connection to a console. All escape
sequences given by the user to console are passed to the server without
interpretation. The server recognizes and processes all escape
sequences.
The conserver parent process will automatically respawn any child
process that dies. The following signals are propagated by the parent
process to its children.
SIGTERM Close all connections and exit.
- SIGHUP Reread the configuration file. New consoles are managed by
- forking off new children, deleted consoles (and their clients) are dropped, and changes to consoles are done "in place", resetting the console port (bringing it down and up) only when necessary. The console name is used to determine when consoles have been added/removed/changed. All actions performed by SIGUSR2 are also performed.
- SIGUSR1 Try to connect to any consoles marked as down. This can come
- in handy if you had a terminal server (or more) that wasn't accepting connections at startup and you want conserver to try to reconnect to all those downed ports.
- SIGUSR2 Close and reopen all console logfiles and, if in daemon mode
- (-d option), the error logfile (see the -L option). All actions performed by SIGUSR1 are also performed.
- Consoles which have no current client connection might produce important error messages. With the -u option, these ``unloved'' errors are labeled with a machine name and output on stdout (or, in daemon mode, to the logfile). This allows a live operator or an automated log scanner to find otherwise unseen errors by watching in a single location.
- Conserver must be run as root if it is to bind to a port under 1024 or if it must read protected password files (like shadow passwords) for authentication (see conserver.passwd(5)). Otherwise, it may be run by any user, with -p used to specify a port above 1024.
- If encryption has been built into the code (--with-openssl), encrypted client connections (without certificate exchanges) happen by default. To add certificate exchanges, use the -c option with the client and server. For authentication of the certificates to work, the signing certificate must be properly trusted, which usually means the public portion is in OPENSSL_ROOT/ssl/certs (on both the client and server sides). See the sample self-signing certificate making script contrib/maketestcerts for further clues. To allow non-encrypted client connections (in addition to encrypted client connections), use the -E option.
OPTIONS
Options may be given as separate arguments (e.g., -n -d) or clustered
(e.g., -nd). Options and their arguments may be separated by optional
white space. Option arguments containing spaces or other characters
special to the shell must be quoted.
- -7 Strip the high bit off of all data received, whether from
- the console client or from the console device, before any processing occurs.
- -atype Set the default access type for incoming connections from
- console clients: `r' for refused (the default), `a' for allowed, or `t' for trusted. This applies to hosts for which no matching entry is found in the access section of conserver.cf(5).
- -bport Set the base port for children to listen on. Each child
- starts looking for free ports at port and working upward, trying a maximum number of ports equal to twice the maximum number of groups. If no free ports are available in that range, conserver exits. By default, conserver lets the operating system choose a free port.
- -ccred Load an SSL certificate and key from the PEM encoded file
- cred.
- -Cconfig Read configuration information from the file config. The
- default config may be changed at compile time using the --with-cffile option.
- -d Become a daemon. Disconnects from the controlling terminal
- and sends all output (including any debug output) to the logfile (see -L).
- -D Enable debugging output, sent to stderr. Multiple -D
- options increases debug output.
- -E If encryption has been built into the code (--with
- openssl), encrypted client connections are a requirement. This option allows non-encrypted clients (as well as encrypted clients) to connect to consoles.
- -F Do not automatically reinitialize failed (unexpectedly
- closed) consoles. If the console is a program (`|' syntax) and it closes with a zero exit status, the console is reinitialized regardless of this option. Without this option, a console is immediately reopened, and if that fails, retried every minute until successful. This option has no effect on the -o and -O options.
- -h Output a brief help message.
- -i Initiate console connections on demand (and close them when
- not used).
- -Llogfile Log errors and informational messages to logfile after
- startup in daemon mode (-d). This option does not apply when not running in daemon mode. The default logfile may be changed at compile time using the --with-logfile option.
- -mmax Set the maximum consoles managed per process. The default
- max may be changed at compile time using the --with-maxmemb option.
- -Mmaster Normally, this allows conserver to bind to a particular IP
- address (like `127.0.0.1') instead of all interfaces. The default is to bind to all addresses. However, if --withuds was used to enable Unix domain sockets for client/server communication, this points conserver to the directory where it should store the sockets. The default master directory (``/tmp/conserver'') may be changed at compile time using the --with-uds option.
- -n Obsolete (now a no-op); see -u.
- -o Normally, a client connecting to a ``downed'' console does
- just that. Using this option, the server will automatically attempt to open (``bring up'') the console when the client connects.
- -Omin Enable periodic attempts (every min minutes) to open
- (``bring up'') all downed consoles (similar to sending a SIGUSR1). Without this option, or if min is zero, no periodic attempts occur.
- -pport Set the TCP port for the master process to listen on. This
- may be either a port number or a service name. The default port, ``conserver'' (typically 782), may be changed at compile time using the --with-port option. If the --with-uds option was used, this option is ignored.
- -Ppasswd Read the table of authorized user data from the file
- passwd. The default passwd may be changed at compile time using the --with-pwdfile option.
- -R Disable automatic client redirection to other conserver
- hosts. This means informational commands like -w and -i will only show the status of the local conserver host and attempts to connect to remote consoles will result in an informative message to the user.
- -S Do not run the server, just perform a syntax check of con
- figuration file and exit with a non-zero value if there is an error. Using more than one -S will cause conserver to output various information about each console in 5 colonseparated fields, enclosed in curly-braces. The philosophy behind the output is to provide information to allow external detection of multiple consoles access the same physical port. Since this is highly environment-specific, conserver cannot do the check internally.
- name The name of the console.
- master The hostname of the master conserver host for the
console.
- aliases The console aliases in a comma-separated list.
- type The type of console. Values will be a `/' for a
- local device, `|' for a command, `!' for a remote port, `%' for a Unix domain socket, and `#' for a noop console.
- details Multiple values are comma-separated and depend on
- the type of the console. Local devices will have the values of the device file and baud rate/parity. Commands will have string to invoke. Remote ports will have the values of the remote hostname and port number. Unix domain sockets will have the path to the socket. Noop consoles will have nothing.
- -u Send unloved console output to conserver's stdout (which,
- in daemon mode, is redirected to the logfile). This applies to all consoles to which no user is attached, independent of whether logging of individual consoles is enabled via conserver.cf entries.
- -Ulogfile Copy all console data to the ``unified'' logfile. The out
- put is the same as the -u output, but all consoles, not just those without a user, are logged. Each line of output is prefixed with the console name. If a user is attached read/write, a `*' is appended to the console name, to allow log watching utilites to ignore potential user-introduced alarms.
- -v Echo the configuration as it is being read (be verbose).
- -V Output the version number and settings of the conserver
- program and then exit.
PROTOCOL
The protocol used to interact with the conserver daemon has two basic
styles. The first style is the initial line-based mode, which occurs
before connecting to a console. The second style is the characterbased, escape-sequence mode, while connected to a console.
The initial line-based mode begins the same for both the master process
and its children. Upon a successful (non-rejected) client connection,
an ``ok'' is sent. The client then issues a command and the server
responds to it with a result string (``ok'' being the sign of success
for most commands). The commands available are ``help'', ``ssl'' (if
SSL was built into the code), ``login'', and ``exit''. Using the
``login'' command, the client authenticates and gains access to the
extended command set. This is where the master process and its children differ. The master process gives the client access to global commands, and the child provides commands for interacting with the consoles it manages. The ``help'' command, in both cases, will provide a
complete list of commands and a short description of what they do.
The second, character-based, style of interaction occurs when the
client issues the ``call'' command with a child process. This command
connects the client to a console and, at that point, relays all traffic
between the client and the console. There is no more command-based
interaction between the client and the server, any interaction with the
server is done with the default escape sequence.
This is, by no means, a complete description of the entire
client/server interaction. It is, however, a brief explanation in
order to give a idea of what the program does. See the PROTOCOL file
in the distribution for further details.
FILES
The following default file locations may be overridden at compile time
or by the command-line options described above. Run conserver -V to
see the defaults set at compile time.
- /etc/conserver.cf description of console terminal lines and
- client host access levels; see conserver.cf(5).
- /etc/conserver.passwd users allowed to access consoles; see con
- server.passwd(5).
- /var/run/conserver.pid the master conserver process ID /var/log/conserver log of errors and informational messages /tmp/conserver directory to hold Unix domain sockets (if
- enabled)
- Additionally, output from individual consoles may be logged to separate files specified in conserver.cf(5).
BUGS
I'm sure there are bugs, I just don't know where they are. Please let
me know if you find any.
AUTHORS
Thomas A. Fine, Ohio State Computer Science
Kevin S Braunsdorf, Purdue University Computing Center
Bryan Stansell, conserver.com