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--- tutorials:remote_access [2011/02/01 02:52] – [ssh] chkuo
+++ tutorials:remote_access [2019/01/11 17:35] (current) – [Key] chkuo
@@ Line 1: / Line 1: @@
 ====== Remote access ======
-===== ssh =====
+===== SSH =====
-==== Log-in ====
+==== Login ====
 ''ssh'' (SSH client) is a program for logging into a remote machine. The typical usage is ''ssh user@hostname'', for example: <code bash>ssh jake@168.192.1.1</code>
@@ Line 16: / Line 17: @@
 You will return to the shell running on your local machine, just like before you logging into the remote server.
-==== ssh key ====
+==== Key ====
-To generate key-pairs, use: <code bash>ssh-keygen -t 'rsa'</code>
+To generate key-pairs, use: <code bash>ssh-keygen -t rsa -b 4096</code>
-This command will create a pair of private key (''~/.ssh/id_rsa'') and public key (''~/.ssh/id_rsa.pub''). To enable authentication on a remote host, append the public key to the ''~/.ssh/authorized_keys'' file in the remote host.
+This command will create a pair of private key (''~/.ssh/id_rsa'') and public key (''~/.ssh/id_rsa.pub''). To enable authentication on a remote host, append the public key to the ''~/.ssh/authorized_keys'' file in the remote host (this file should be owned by the user and have the ''644'' permissions).
+If the home directory is encrypted, ''authorized_keys'' would not work while within the home directory before the user is logged in. Move the ''authorized_keys'' file and modify ''/etc/ssh/sshd_config'' accordingly.
+For example (see [[https://help.ubuntu.com/community/SSH/OpenSSH/Keys#Troubleshooting]]:
+  * set up ''/etc/ssh/<username>'' (owned by user, 755 permissions).
+  * in ''/etc/ssh/sshd_config'', add ''AuthorizedKeysFile    /etc/ssh/%u/authorized_keys''
+  * restart sshd: ''sudo service ssh restart''
-===== scp =====
+==== Keep alive ====
-''scp'' copies files between hosts on a network. The typical usage is ''scp user@host1:file1 user@host2:file2''. Similar to the example in ssh, the username can be omitted if it is the same in the two hosts; in addition, the local host can be omitted as well.
+To prevent the ssh sessions from being disconnected due to inactivity, add the following lines to ''/etc/ssh_config'' on the client:
+<code>
-For example, to copy a file (foo.txt) from the home directory (~) to the home directory in the remote server, use:
+ServerAliveInterval 60
-<code bash>
+ServerAliveCountMax 60
-$ scp ~/foo.txt 168.192.1.1:~
 </code>
+This sends a signal every 60 seconds for a maximum of 60 times (one hour) from the client to the server.
-Reversely, to copy the file from the remote server back to the local workstation:
+If you do not have the permission to make this modification, put those lines to ''~/.ssh/config'' (create the file is necessary).
-<code bash>
-$ scp 168.192.1.1:~/foo.txt ~
-</code>
+===== SCP =====
+''scp'' copies files between hosts on a network. The typical usage is: <code bash>scp user@host1:file1 user@host2:file2</code>
+Similar to the example in ssh, the username can be omitted if it is the same in the two hosts; in addition, the local host can be omitted as well.
+For example, to copy a file (foo.txt) from the home directory (~) of the local workstation to the home directory in the remote server, use: <code bash>scp ~/foo.txt 168.192.1.1:~</code>
+Reversely, to copy the file from the remote server back to the local workstation, use: <code bash>scp 168.192.1.1:~/foo.txt ~</code>
 Some commonly used options include:
@@ Line 39: / Line 52: @@
   * ''-r'': Recursively copy entire directories.
-For example, to preserve the property of the file being copied, use:
+For example, to preserve the property of the file being copied, use: <code bash>scp -p ~/foo.txt 168.192.1.1:~</code>
-<code bash>
-$ scp -p ~/foo.txt 168.192.1.1:~
-</code>
-To copy an entire directory:
-<code bash>
-$ scp -r ~/foo_dir 168.192.1.1:~
-</code>
+To copy an entire directory, use: <code bash>scp -r ~/foo_dir 168.192.1.1:~</code>