To download a repository hosted on github
git clone git@github.com:account_name/repo_name.git
The git@github.com:account_name/repo_name.git will be shown on the home page for the repository on github.com
To update your code from the master branch of the repo:
git pull origin master
To commit the changes you have made locally:
git commit -m "the message explaining what these code changes did"
To send your changes to the repo at github:
git push origin master
Host keys are used to security log into remote servers (such as Virtual Private Servers – VPS). With Ubuntu if you are using host keys to sign into servers securely and have asked for strict checking, if you make a change (such as rebuilding your VPS) the host key will change and you cannot login and will get a message like:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
…
Please contact your system administrator.
…
RSA host key for 128.0.0.128 has changed and you have requested strict checking.
Host key verification failed.
if that happens you need to remove your local host key. Then you can sign back in and you will be able to save a new copy of the host key. If you don’t know why the key has changed you should figure that out first as it maybe be an indication of an important security problem. To remove you local key, you can use ssh-keygen -R [ip address of server with the bad key] for example: ssh-keygen -R 128.0.0.128
Then when you try to sign in you will get
The authenticity of host '128.0.0.128 (128.0.0.128)' can't be established. RSA key fingerprint is ed:...:ea. Are you sure you want to continue connecting (yes/no)?
And if you know why (such as you made changes to the server) you can say yes and connect and save the new known host key.
add a user: sudo adduser [newuser]
sudo adduser john
then give password, and setup home folder,when prompted
edit the list of super users
visudo
list users
cat /etc/passwd
change password of a user – sudo passwd [username]
sudo passwd john
to change your password you can just use sudo passwd.
delete user
sudo deluser username
This will not delete the home folder (and subfolder) those must be dealt with separately. A new user created with the old user name would have access to those files.
temporarily lock a user account – Simply locking a user account will not prevent a user from logging into your server remotely if they have previously set up RSA public key authentication.
sudo passwd -l username
To unlock the account
sudo passwd -u username
Groups are used in to control permissions (see file permissions)
add user to a group
usermod -G [group-name] [username]
usermod -G basketball john
using the -G switch ads the group as a supplemental group. Using -g would make the group that users primary group.
see what groups a user is in
id john
add a new group: groupadd [new_group_name]
groupadd ruby_developers
Tips on how to improve the performance of your MySQL Server.
Also see: Basic MySQL Performance Monitoring
MySQLTuner can identify the fragmented table count. To defragment all the tables on the MySQL database server
sudo mysqlcheck --optimize -A -uroot -p
MySQLTuner will also provide suggested adjustments to my.cnf.