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“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 653 — #679

Security in the Network

Furthermore, ssh offers the possibility to run commands on remote sys-

tems, as known from rsh. In the following example, run the command

uptime on the host sun and create a directory with the name tmp/. The

program output is displayed on the local terminal of the host earth.

ssh otherplanet "uptime; mkdir tmp"

tux@otherplanet’s password:

1:21pm up 2:17, 9 users, load average: 0.15, 0.04, 0.02

Quotation marks are necessary here to send both instructions with one

command. It is only by doing this that the second command is executed

on sun.

26.4.3 scp — Secure Copy

scp copies ﬁles to a remote machine. It is a secure and encrypted sub-

stitute for rcp. For example, scp MyLetter.tex sun: copies the ﬁle

MyLetter.tex from the host earth to the host sun. If the user name on

earth is different than the user name on sun, specify the latter using the

username@host format. There is no -l option for this command.

After the correct password is entered, scp starts the data transfer and

shows a growing row of asterisks to simulate a progress bar. In addi-

tion, the program displays the estimated time of arrival to the right of the

progress bar. Suppress all output by giving the option -q.

scp also provides a recursive copying feature for entire directories. The

command scp -r src/ sun:backup/ copies the entire contents of the

directory src/ including all subdirectories to the backup/ directory on

the host sun. If this subdirectory does not exist yet, it is created automati-

cally.

The option -p tells scp to leave the time stamp of ﬁles unchanged. -C com-

presses the data transfer. This minimizes the data volume to transfer, but

creates a heavier burden on the processor.

26.4.4 sftp — Secure File Transfer

The sftp program can be used instead of scp for secure ﬁle transfer. During

an sftp session, you can use many of the commands known from ftp. The

sftp program may be a better choice than scp, especially when transferring

data for which the ﬁle names are unknown.

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SUSE LINUX Enterprise Server