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→Common SSH Problems
[[Category:SPO600]]
<!-- {{Admon/important|Backup Your Data|These computers are NEVER backed up. Please save all important files on other storage. '''These machines may fail, be removed, be upgraded, or be reinstalled at any time.'''}}In [[SPO600]], remote access to servers is provided for learning and project work. It is recommended that you also set up [[SPO600 Host Setup|a personal Linux system]].-->
== Preparatory Steps ==
In order to gain access to these computers, you must send an [[SSH]] key to your [[User:Chris Tyler|professor]]. <!-- Please follow these instructions exactly:
# Follow the steps outlined under [[SSH#Using_Public_Keys_with_SSH|Using Public Keys with SSH]] to create your key.
# Copy the public key (<code>id_rsa.pub</code> or <code>id_dsa.pub</code>) to a file named <code>''yourUserId''.pub</code> -- for example, if your chosen user ID is "jldoe", save the key in the file <code>jdoe.pub</code> using a command such as: <code>cp ~/.ssh/id_rsa.pub ''jdoe''.pub</code>
# Attach that file to an e-mail message and send it to [mailto:chris.tyler@senecacollege.ca chris.tyler@senecacollege.ca] with the subject line "SPO600 Key".-->
An account will be created within a few work days of sending the key.
{{Admon/tip|Check Your Key!|Your professor uses an automated script to create accounts, so the key must be valid, in the OpenSSH format, and correctly named in order to work successfully.}}
== Available Servers ==
<!-- {{Admon/important|Content being Updated|This page is in the process of being updated from a previous semester's content. The SPO600 servers will be set up in a new configuration later this semester, and this information will be updated. Do not rely on this information until this warning is removed.}} {{Admon/important|Server Changes for Fall 2019|The server configuration for Fall 2019 has configurations have changed several times -- previous mentions of these systems by name may have referred to different hardware. Note that additional servers may be added or removed as the semester proceeds.}}--> The names of servers within CDOT are based on the names of countries. There is no significance to the country names.
=== AArch64: israel.cdot.systems ===
If you're using a command-line ssh system, you can issue a command such as this:
If you're using a command-line ssh system, you can issue a command such as this:
ssh -p 2200 2205 ''username''@ehl.cdot.systems === AArch64: israel === A different AArch64 system is ''israel''. This machine has a good number of mid-level cores. This system is located outside of the EHL and can be reached directly:
ssh ''username''@israel.cdot.systems
-->
=== x86_64: xerxes portugal.cdot.systems ===
The x86_64 server system is known as ''xerxesportugal''. If you're using a command-line ssh system, you can access xerxes with a command such as this:
ssh ''username''@xerxesportugal.cdot.systems
== Simplified SSH Access ==
Host "xerxes"
hostname "xerxes.cdot.systems"
user "YourUserId" -->
Host "aarchie"
port 2200
Host "ccharlie" hostname "ehl.cdot.systems" user "YourUserID" port 2205--> Host "portugal" hostname "portugal.cdot.systems" user "YourUserID" Host "israel" hostname "israel.cdot.systems" user "YourUserID" <!-- Host "xerxes"
hostname "xerxes.cdot.systems"
user "YourUserID"
-->
Once you have added these lines (inserting your user ID where appropriate) and set the permission on that file (<code>chmod 0600 ~/.ssh/config</code>) you can use these commands to access the servers:
ssh aarchie ssh bbettyisrael
ssh xerxesportugal
You can similarly configure simplified access in most other SSH client programs.
{{Admon/caution|Danger! Use Superuser privilege at your Own Risk.|Note that the use of the superuser account via <code>sudo</code> removes almost all restrictions on what you can do. It is easily possible for you to completely destroy the operating system! Take your time, double-check your commands, and if in doubt, ask. Be aware that your actions may affect other users and vice-versa.}}
{{Admon/caution|Do Not DO NOT Build or Install Software Except Via as Root except via RPM (dnf/yum) or DEB (apt)|Do not build or install software as the root user (using <code>sudo</code>), except in RPM or DEB form using the <code>dnf</code>/<code>yum</code> or <code>yumapt</code> commands(as appropriate to the system). Building or installing software as root may overwrite system files and be very difficult to track down.<br /><br />It is OK to install software into your own directories (e.g., <code>~/bin</code> or <code>~/local</code>), which can be done without root privilege.}}
In order to use <code>sudo</code>, you will need to know your password. An initial random password is provided in the file <code>~/password.txt</code> (note that your password will be different on each server). Feel free to change this with the <code>passwd</code> command -- not by editing the file, which is provided only for your information!
== Multiuser SSH Access from Other Client Systems == If you wish to access the servers from additional computers, you can append the SSH public keys from those computers to the <code>~/.ssh/authorized_keys</code> file. Alternately, you can copy the private key from one client system to another (e.g., your laptop to your desktop). == OS Versions ==
# If your SSH public key is not named <code>~/.ssh/id_rsa</code>, your SSH client may not automatically find it. You can specify the identity (private key) file using the <code>-i</code> argument to the SSH command.}}
The passphrase is the one you provided when you created your SSH keys. You must remember this passphrase in order to successfully unlock your private key. If you do not remember your passphrase, you will need to create a new pair of keys and re-send the public key to your professor:
# Create the keys with <code>ssh-keygen -t ed25591</code>
# Copy the public key (which by default will be named <code>~/.ssh/id_ed25519.pub</code>) to a file named <code>'''UserId'''.pub</code> where '''UserId''' is your Seneca User ID.
# Attach that file to an e-mail message and send it to your professor.
===== Situation 2: The SSH client asks you for a password =====
The password is for the remote system, but the SSH client will only ask you for a password if it is unable to authenticate using your keys. If that is the case, then one of your keys is corrupted, missing, has the wrong permission, or can't be found by the SSH client.
# If you're using OpenSSH, try using the <code>-i</code> argument to tell the client which private key identity file to use: <code>ssh -i /path/to/ssh/PrivateKey ...</code>
# Check the permissions on the private key and the directory holding the private key.
# If necessary, generate a new key and send it to your professor (see the previous section).
===== Getting Verbose Output =====
To see what the OpenSSH client program is doing, you can use the <code>-v</code> (verbose) argument, up to three times: <code>ssh -vvv ...</code>
By reading through the output carefully, you can see what the OpenSSH client program is doing, and address any problems that arise (such as permission or file naming issues).
== Disconnect/Reconnect Ability ==
The [[Screen Tutorial|screen]] utility provides disconnect/reconnect capability, which is very useful for unstable network connections, long interactive operations, and changing your work location.
Other programs such as tmux provide similar capability.
For graphical disconnect/reconnect capability, consider using VNC.
