Remote Access

For transfering large amounts of data to and from users outside of CAL, see Transferring Large Data.

Secure Shell (SSH)

To access your workstation remotely, use SSH. Our CAL linux network can be access through the following shell servers:

saturn.astro.columbia.edu (this requires a ssh key-pair or GSSAPI/kerberos authentication)

pluto.astro.columbia.edu (this only requires your CAL unix password)

venus.astro.columbia.edu (temporarily, this only requires your CAL unix password)

A good method of securing your workstation as well as the overall network is to generate a ssh key-pair .Please note that both the Linux and Sun workstations do not accept incoming ssh protocol 1 connections, only ssh protocol 2 connections.

A remote host running ssh can be accessed with:

  ssh remote_host

where remote_host is the fully qualified host name (e.g. for host jewels this is jewels.phys.columbia.edu), or its IP number. This command assumes that you have the same username on both systems, but in the case where this is not so:

  ssh -l remote_username remote_host

where remote_username is obviously your username on the remote host. Note, if this is your first access to the remote host, then you're unlikely to have its public key, and hence ssh will inform you of this e.g. The authenticity of host 'pirates.phys.columbia.edu (128.59.168.143)' can't be established.

RSA key fingerprint is 5c:5b:17:2f:55:57:be:3e:04:41:90:62:2f:2a:ac:97.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'mraos.ra.phy.cam.ac.uk,131.111.48.8' (RSA) to the
list of known hosts.
The public key of the remote host has been added to the file ~/.ssh/known_hosts in your account. 

As a result, this message will not be displayed in future ssh connections to this host. As shown in a section above, you can generate your own public key(s) between your different accounts using ssh-keygen, and overcome the problem regarding the lack of the public key of the remote host. Copy the newly generated public key from the account on one system to the ~/.ssh/authorized_keys file on the other. Transfering public keys between accounts can simply be done via email, as the public key is just a long line of text, which can then be extracted from the mail message (make sure to preserve its line length) and added to the appropriate file.

Using sftp

sftp, and scp (discussed below) both come into their own for file transfers between user accounts at different institutions. sftp (Secure File Transfer) is a ftp-like client that runs over an ssh tunnel, and that can be used in file transfer over the network. It does not use the FTP daemon (ftpd or wu-ftpd) for connections, allowing a significant improvement in the system security. sftp does not support anonymous logins. A user account is required on the remote end. sftp and scp do not require any dedicated daemon since the two programs connect to sshd servers. Let's suppose that you would connect via sftp to your account myname on host1. In order to do that use the command:

sftp myname@host1

When sftp is ready to accept commands, it will display a prompt sftp>. In the sftp manual page there are a complete list of the commands which the user can use:

quit

Quits from the application

cd directory

Changes the current remote working directory.

lcd directory

Changes the current local working directory.

ls [ -R ] [ -l ] [ file ... ]

Lists the names of the files on the remote server.

lls [ -R ] [ -l ] [ file ... ]

Same as ls, but operates on the local files.

get [ file ... ]

Transfers the specified files from the remote end to the local end. Directories are recursively copied with their contents.

put [ file ... ]

Transfers the specified files from the local end to the remote end. Directories are recursively copied with their contents.

mkdir dir (rmdir dir)

Tries to create (delete) the directory specified in dir. e.g. while logged into cass06 get /etc/inet/hosts from cass56:

cass06% sftp cass56
Connecting to cass56...
username@cass56's password: 
sftp> pwd
Remote working directory: /home/username
sftp> cd /etc/inet
sftp> pwd
Remote working directory: /etc/inet
sftp> ls     
...
-rw-r--r--   1 root     other        140 Jan 14 09:42 hosts
...
sftp> get hosts
Fetching /etc/inet/hosts to hosts
sftp> lls
hosts

sftp> quit