Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Remove a document in a collection in MongoDB
Answer:
If you want to remove a document in the test collection, with a key "name" equal to "Peter", you can execute the following command in the MongoDB Interactive Shell.
db.test.remove( { name : "Peter" } )
Done.
How to change the MySQL temporary directory
Answer:
To change the temporary directory of your MySQL server to use a non-default directory, you can change the tmpdir parameter in your my.cnf
..
tmpdir = /data/tmp
..Don't forget to change the permission of that temporary directory
# sudo chmod mysql:mysql /data/tmp
Then restart MySQL to take effect.
# /sbin/service mysqld restart
Delete files permanently with shred command
Answer:
Sometimes we might need to delete files and don't want it can be recovered.
To do so, use the shred command.
# shred -v -n 10 -u -z test.txt
The above command will overwrite the file 10 times before deleting it.
Alter all tables in MySQL
Answer:
To alter all the tables in a given database in MySQL, e.g. change the storage engine, you can first generate the SQL statements using following method.
mysql> select CONCAT("Alter Table `", TABLE_SCHEMA,"`.`", TABLE_NAME, "` ENGINE = InnoDB") AS cmd from TABLES where TABLE_SCHEMA = "test";
It will print out the followings:
+----------------------------------------------------------------+
| cmd |
+----------------------------------------------------------------+
| Alter Table `test`.`foo` ENGINE = InnoDB |
| Alter Table `test`.`bar` ENGINE = InnoDB |
...
Then you can execute the above commands manually.
Remove added files using svn add
Answer:
To remove files from committed into the SVN in the next commit if you have just added them using the svn add, you should use svn revert
e.g.
# svn revert file.txt
