Commands Reference, Volume 4

rshd Daemon

Purpose

Provides the server function for remote command execution.

Syntax

/usr/sbin/rshd [ -c ] [ -s ]

Description

The /usr/sbin/rshd daemon is the server for the rcp and rsh commands. The rshd daemon provides remote execution of shell commands. These commands are based on requests from privileged sockets on trusted hosts. The shell commands must have user authentication. The rshd daemon listens at the socket defined in the /etc/services file.

Changes to the rshd daemon can be made using the System Management Interface Tool (SMIT) or System Resource Controller (SRC), by editing the /etc/inetd.conf or /etc/services file. Entering rshd at the command line is not recommended. The rshd daemon is started by default when it is uncommented in the /etc/inetd.conf file.

The inetd daemon get its information from the /etc/inetd.conf file and the /etc/services file.

After changing the /etc/inetd.conf or /etc/services file, run the refresh -s inetd or kill -1 InetdPID command to inform the inetd daemon of the changes to its configuration file.

Service Request Protocol

When the rshd daemon receives a service request, it initiates the following protocol:

1. The rshd daemon checks the source port number for the request. If the port number is not in the range 0 through 1023, the rshd daemon terminates the connection.
2. The rshd daemon reads characters from the socket up to a null byte. The string read is interpreted as an ASCII number (base 10). If this number is nonzero, the rshd daemon interprets it as the port number of a secondary stream to be used as standard error. A second connection is created to the specified port on the client host. The source port on the local host is also in the range 0 through 1023.
3. The rshd daemon uses the source address of the initial connection request to determine the name of the client host. If the name cannot be determined, the rshd daemon uses the dotted decimal representation of the client host's address.
4. The rshd daemon retrieves the following information from the initial socket:
   • A null-terminated string of at most 16 bytes interpreted as the user name of the user on the client host.
   • A null-terminated string of at most 16 bytes interpreted as the user name to be used on the local server host.
   • Another null-terminated string interpreted as a command line to be passed to a shell on the local server host.
5. The rshd daemon attempts to validate the user using the following steps:
   1. The rshd daemon looks up the local user name in the /etc/passwd and /etc/security/passwd file and checks to see if the password, and therefore the user, has expired. It also verifies that the encrypted password string is valid and tries to switch to the home directory (using the chdir subroutine). If either the lookup or the directory change fails, the rshd daemon terminates the connection.
   2. If the local user ID is a nonzero value, the rshd daemon searches the /etc/hosts.equiv file to see if the name of the client workstation is listed. If the client workstation is listed as an equivalent host, the rshd daemon validates the user.
   3. If the $HOME/.rhosts file exists, the rshd daemon tries to authenticate the user by checking the .rhosts file.
   4. If either the $HOME/.rhosts authentication fails or the client host is not an equivalent host, the rshd daemon terminates the connection.
6. After rshd validates the user, the rshd daemon returns a null byte on the initial connection and passes the command line to the user's local login shell. The shell then inherits the network connections established by the rshd daemon.

The rshd daemon should be controlled using the System Management Interface Tool (SMIT) or by changing the /etc/inetd.conf file. Typing rshd at the command line is not recommended.

Manipulating the rshd Daemon with the System Resource Controller

The rshd daemon is a subserver of the inetd daemon, which is a subsystem of the System Resource Controller (SRC). The rshd daemon is a member of the tcpip SRC subsystem group. This daemon is enabled by default in the /etc/inetd.conf file and can be manipulated by the following SRC commands:

Flags

Examples

1. To start the rshd daemon, type the following:
   startsrc -t shell
   This command starts the rshd subserver.
2. To stop the rshd daemon, type the following:
   stopsrc -t shell
   This command allows all pending connections to start and existing connections to complete but prevents new connections from starting.
3. To force stop the rshd daemon and all rshd connections, type the following:
   stopsrc -t -f shell
   This command terminates all pending connections and existing connections immediately.
4. To display a short status report about the rshd daemon, type the following:
   lssrc -t shell
   This command returns the daemon's name, process ID, and state (active or inactive).

Related Information

The kill command, lssrc command, refresh command, rsh command, startsrc command, stopsrc command.

The inetd daemon.

The $HOME/.rhosts file format, /etc/hosts.equiv file format, /etc/inetd.conf file format, /etc/services file format.

The rcmd subroutine.

TCP/IP Daemons in AIX 5L Version 5.2 System Management Concepts: Operating System and Devices.