Technical data

• RCP – Allows files to be copied between remote hosts.
• RLOGIN — Provides interactive access to remote hosts.
• RSH — Passes a command to a remote host for execution.
• REXEC – Authenticates and executes RCP and other commands.
• RMT/RCD – Provides remote access to magnetic tape and CD-ROM drives.
In addition to password authentication, the R commands use a system based on
trusted hosts and users. Trusted users on trusted hosts are allowed to access the
local system without providing a password.
Trusted hosts are also called equivalent hosts because the software assumes that
users who have access to a remote host should be given equivalent access to the
local host. The system assumes that user accounts with the same name on both
hosts are ‘‘owned’’ by the same user. For example, the user logged in as BETHANY
on a trusted system is granted the same access as a user logged in as BETHANY
on the local system.
This authentication system requires databases that define the trusted hosts and
the trusted users. On UNIX systems, these databases are:
•
/etc/hosts.equiv
— defines the trusted hosts and users for the entire
system.
•
rhosts
— defines the trusted hosts and users for an individual user account.
This file is located in the user’s home directory.
On OpenVMS hosts, the proxy database TCPIP$PROXY.DAT defines trusted hosts
and trusted users for the entire system.
Each of these topics is covered in detail in the Compaq TCP/IP Services for
OpenVMS Management guide.
5.4.4 Differences Between FTP and RCP
Unlike FTP, the RCP protocol provides no method of transferring file type
information between the sender and the recipient. It transfers only length, a
modified and created timestamp, protection mode, and the byte stream of file data.
As a result, RCP is unable to determine the file type of a file it receives.
To revert the file type to a usable format in transfers between OpenVMS systems,
if the original file is fixed length or undefined, you can change the attributes on
the Stream_LF copy to correspond to the format of the original file. To do so, enter
the DCL command SET FILE in the following format:
SET FILE/ATTR=
(file-attribute[,...])
For example, the following command transfers an OpenVMS executable image file
(with a fixed record length of 512-bytes, and makes the file executable again.
$ SET FILE/ATTR=(rfm:fix, lrl:512) rcp-copied-file.exe
You can also use a logical name to change the behavior set by the options.
Although RCP uses secure authentication for security, it has file size limitations
that FTP does not have. FTP has no security; passwords are sent in ASCII. RCP
sends only the length of the file (in ASCII format). OpenVMS interprets this length
as a signed 32-bit integer. Therefore, files transferred using RCP must no more
than (2 GB -1) bytes (0x7FFFFFF=2147483647 bytes or roughly 1 byte less than
4194304 RMS 512 byte blocks).
Network Server Services 5–11