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remshd(1m) [hpux man page]

remshd(1M)																remshd(1M)

NAME
remshd - remote shell server SYNOPSIS
In Kerberos V5 Network Authentication Environments DESCRIPTION
The command is the server for the and commands, and the function in case of IPv6 systems (see rcp(1), rdist(1), remsh(1), rcmd(3N), and rcmd_af(3N)). allows two kinds of authentication methods: 1. Authentication based on privileged port numbers where the client's source port must be in the range 512 through 1023. In this case assumes it is operating in normal or non-secure environment. 2. Authentication based on Kerberos V5. In this case assumes that it is operating in a Kerberos V5 Network Authentication, i.e., secure environment. The daemon invokes if a service request is received at ports indicated by or services specified in (see inetd(1M) and services(4)). Ser- vice requests arriving at the port assume a secure environment and expect Kerberos authentication to take place. To start from the daemon in a non-secure environment, the configuration file must contain an entry as follows: In a secure environment, must contain an entry: The configuration lines above will start in mode. To run in mode, the following line must be present in the file: That is, for IPv6 applications, the protocol has to be changed to See inetd.conf(4) for more information. To prevent non-secure access, the entry for should be commented out in Any non-Kerberos access will be denied since the entry for the port indicated by has now been removed or commented out. In such a situation, a generic error message, is displayed. See for more details. Note that by commenting out the entry for the port, access by other clients such as will also be prevented. Options recognizes the following options. Forbid authentication based on the user's file unless the user is a superuser. Disable transport-level keep-alive messages. Otherwise, the messages are enabled. The keep-alive messages allow sessions to be timed out if the client crashes or becomes unreachable. With this option enabled, returns immediately after its child process gets killed; it does not wait for all its sub child processes to die. This in turn makes not wait even when the sub child processes are running remotely. As a result, will not appear hung. It is recom- mended that users do not use the option if they want to wait until the completion of all the sub child processes. Otherwise, the user may get an unexpected result. This option is applicable only to with a secondary socket connection. Note that even with the option enabled, will exit if command standard error is closed. This option is used in multi-homed NIS systems. It disables from doing a reverse lookup of the client's IP address; see gethostbyname(3N). It can be used to circumvent an NIS limita- tion with multi-homed hosts. In a secure environment, will recognize the following additional options: Ignore checksum verification. This option is used to achieve interoperability between clients and servers using different checksum calculation methods. For example, the checksum calcu- lation in an application developed with Kerberos V5 Beta 4 API is different from the calculation in a Kerberos V5-1.0 appli- cation. Authorization based on Kerberos V5 must succeed or access will be rejected (see sis(5) for details on authorization). Authentication based on privileged port numbers and authorization of the remote user through equivalent accounts must succeed. For more information on equivalent accounts, see hosts.equiv(4). Either one of the following must succeed. The order in which the authorization checks are done is as specified below. 1. Authentication based on privileged port numbers and authorization of the remote user through equivalent accounts (see hosts.equiv(4)). 2. Authorization based on Kerberos V5. Either one of the following must succeed. The order in which the authorization checks are done is as specified below. 1. Authorization based on Kerberos V5. 2. Authentication based on privileged port numbers and authorization of the remote user through equivalent accounts. Note: The option is ignored when used with and the option is ignored when used with The default option is Operation When receives a service request, it responds with the following protocol: 1. The server checks the client's source port. If the port is not a privileged port, that is, in the range 512 through 1023, and is operating in a non-secure environment, the connection is terminated. In a secure environment, the action taken depends on the command line options: The source port must be a privileged port otherwise the connection is terminated. If the source port is not a privileged port then authorization based on Kerberos must succeed or the connection is terminated. The source port must be a privileged port if Kerberos authorization fails. No action is taken. 2. The server reads characters from the connection up to a null byte. It interprets the resulting string as an ASCII number, base 10. 3. If the number is non-zero, it is interpreted as the port number of a secondary stream to be used for standard error. A sec- ond connection is then created to the specified port on the client's host. (The source port of this second connection will also be checked as specified in item 1.) If the first character sent is a null no secondary connection is made, and the standard error from the command is sent to the primary stream. If the secondary connection has been made, interprets bytes it receives on that socket as signal numbers and passes them to the command as signals. See signal(2). 4. The server checks the client's source address and requests the corresponding host name (see named(1M), gethostbyaddr(3N), and hosts(4)). If it cannot determine the hostname, it uses the dot-notation representation of the host address. 5. In a secure environment performs authentication based on Kerberos V5. See sis(5) for details. 6. The server reads the client's host account name from the first connection. This is a null-terminated sequence not exceeding 256 characters. 7. The server reads the server's host account name from the first connection. This is a null-terminated sequence not exceeding 256 characters. 8. The server reads a command to be passed to the shell from the first connection. The command length is limited by the maximum size of the system's argument list. 9. then validates the user as follows (all actions take place on the host runs on): a. It looks up the user account name (retrieved in step 6) in the password file. If it finds it, it performs a to the user's home directory, if there is one, or to "/." b. If either the lookup or fails, the connection is terminated (see chdir(2)). c. The connection is also terminated if o the account accessed is administratively locked. The account can be locked by entering a character in the pass- word field that is not part of the set of digits (such as *). The characters used to represent "digits" are `.' for 0, / for 1, 0 through 9 for 2 through 11, `A through Z' for 12 through 37, and `a through z' for 38 through 63. (See also passwd(4)). o in a non-secure environment, the account accessed is protected by a password and, either the password expired or the account on the client's host is not equivalent to the account accessed. o in a secure environment, the command line options decide whether connection is to be terminated. if Kerberos authorization does not succeed the connection is terminated (see sis(5) for details on authorization). if the client's host is not equivalent to the account accessed, the connection is terminated. if the account is not equivalent to the account accessed, then Kerberos authorization has to succeed or the connection is ter- minated. if Kerberos authorization fails, then the account has to be equivalent or the connection is terminated. For more information on equivalent accounts, see hosts.equiv(4). 10. A null byte is returned on the primary connection and the command line is passed to the normal login shell of the user with that shell's option. The shell inherits the network connections established by and assumes the normal user and group permis- sions of the user. uses the following path when executing the specified command: 11. If a secondary socket has been set up, normally exits when command standard error and secondary socket standard error have both been closed. If no secondary socket was set up, has called an function, launched the command process, and is no longer present. SECURITY FEATURES
For detailed information on all the configuration parameters that affect see security(4). supports the following configuration parameters in the file: o o DIAGNOSTICS
All diagnostic messages are returned on the connection associated with standard error 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 9 above upon successful completion of all the steps before the command execution). The first socket connection does not use a reserved port or the client's host address is not an Internet address. Unable to complete the connection of the secondary socket used for error communication. The secondary socket connection does not use a reserved port. The name of the user account on the client's host is longer than 256 characters. The name of the user on the server's host is longer than 256 characters. The command line passed exceeds the size of the argument list (as configured into the system). No password file entry existed for the user name on the server's host, or the authentication procedure described above in step 8 failed. The command to the home directory or "/" on the server's host failed. The pipe needed for the standard error output wasn't created. The server was unable to fork a process to handle the incoming connection. Wait a period of time and try again. If this message persists, the server's host may have runaway processes that are using all the entries in the process table. Error in executing the named system call. The message specifies the cause of the failure. The user's login shell could not be started. This message is returned on the connection associated with the standard error and is not preceded by a leading byte with a value of 1. Other messages can be returned by the remote command when it executes. This generic message could be due to a number of reasons. One of the reasons could be because the entry for shell service is not present in This entry may have been removed or commented out to prevent non-secure access. Kerberos specific errors are listed in sis(5). WARNINGS
The integrity of each host and the connecting medium is assumed if the "privileged port" authentication procedure is used in a non-secure environment or if the command line options are used in a secure environment. Although both these methods provide insecure access, they are useful in an "open" environment. Note that all the information, including any passwords, are passed unencrypted between the two hosts when is invoked in a non-secure envi- ronment. ignores and so these signal numbers can safely be sent to remote commands via the secondary socket provided by Other signal numbers may cause to kill itself. AUTHOR
was developed by the University of California, Berkeley. FILES
User's private equivalence list List of equivalent hosts SEE ALSO
rcp(1), rdist(1), remsh(1), inetd(1M), named(1M), chdir(2), signal(2), gethostbyaddr(3N), gethostbyname(3N), rcmd(3N), rcmd_af(3N), hosts(4), hosts.equiv(4), inetd.conf(4), inetd.sec(4), passwd(4), security(4), services(4), sis(5). remshd(1M)
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