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 the startup time of a particular program
Answer:
E.g. To check the startup time of MySQL server:
# ps -eo pid,user,cmd,lstart | grep /sbin/mysqld
3546 mysql /usr/sbin/mysqld --basedir= Tue Mar 30 21:29:12 2010
9195 root grep /sbin/mysqld Tue Mar 30 22:43:33 2010
Repeat previous command in Bash
Answer:
It is easy to type !! when you want to repeat the previous executed command in Bash
# ls -l /var/log/messages
-rw-r----- 1 syslog adm 330 Mar 29 17:17 /var/log/messages
# !!
ls -l /var/log/messages
-rw-r----- 1 syslog adm 330 Mar 29 17:17 /var/log/messages
Packet sniffing with tcpdump
Answer:
To perform packet sniffing, it is easy with tcpdump
# tcpdump -i eth0 -w dump.cap -s 0After you terminated the tcpdump, you can use tool such as Wireshark to analyse the dump.cap.
Find out which programs are listening TCP port
Answer:
Use the command: netstat -tlnp
# netstat -tlnp
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:443 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN
Save a file in vim without the needed permissions
Answer:
Very often, you opened a file using vim, edited it and find out that the file is opened as read only, i.e. you don't have permission to make any change(s).
What will you do? Simplest method is to save it into a temp file and rename it afterward.
However, there exist a simple method that allow you to save the file anyway.
Instead of using :wq, you enter the following.
:w !sudo tee %
That is what you need.
