Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
How to check failed login attempt in Ubuntu
Answer:
Every login attempts are logged in the file /var/log/auth.log in Ubuntu.
To check failed login attempt(s),
E.g.
# grep 'Failed password' /var/log/auth.log
Jan 31 14:00:27 localhost sshd[16141]: Failed password...
Jan 31 14:00:46 localhost sshd[16141]: Failed password...
Jan 31 14:00:49 localhost sshd[16141]: Failed password...
Prepare statement in MySQL
Answer:
MySQL 5.1 provides support for server-side prepared statements, allow you to code more efficient database driven program.
Example:
mysql> PREPARE stmt_password FROM 'SELECT password(?)';
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> SET @a = 1;
Query OK, 0 rows affected (0.00 sec)
mysql> EXECUTE stmt_password USING @a;
+-------------------------------------------+
| password(?) |
+-------------------------------------------+
| *E6CC90B878B948C35E92B003C792C46C58C4AF40 |
+-------------------------------------------+
1 row in set (0.00 sec)
mysql> SET @a = 2;
Query OK, 0 rows affected (0.00 sec)
mysql> EXECUTE stmt_password USING @a;
+-------------------------------------------+
| password(?) |
+-------------------------------------------+
| *12033B78389744F3F39AC4CE4CCFCAD6960D8EA0 |
+-------------------------------------------+
1 row in set (0.00 sec)
As you can see above, once you have prepared the statement in server, you can reuse the statement by injecting a new value. It is faster since MySQL only need to one time SQL statement parsing, rather than parse your SQL statement every time and execute.
How to broadcast text message to all users
Answer:
To broadcast message on the terminals of all currently logged in users, use the wall command
# echo "Hello" | wall
Execute command as another user
Answer:
If you want to run command as another user, you can use the following method:
# sudo su mark -c 'whoami'
mark
Assume currently logged in as user other than mark.
How to check Linux I/O scheduler
Answer:
Assume your hard drive is sda, you can check the current Linux I/O scheduler at
# cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]
Above shows that you are currently using the cfq scheduler.
