Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Disable IPv6 in Linux
Answer:
To disable IPv6 during boot time.
1. edit /boot/grub/menu.lst
# sudo vi /boot/grub/menu.lst
2. append the following line at the end of your targeted kernel, save the file.
ipv6.disable=1
3. Restart your system and verify to see it is now disabled (The following command should return nothing)
# ip a | grep inet6
How to comment out a large block of lines in vi?
Answer:
Press enter and that's all.
How to safety delete a file in Linux?
Answer:
Sometimes, you might have a very sensitive file that don't want others to recover, you might want to use the following command
shred -u password.txt
The command will overwrite the password.txt repeatedly, in order to make it harder for data recovery, and finally delete it.
Permission denied when redirection with sudo
Answer:
When you are doing redirection with sudo, such as the following command
# sudo echo 1 > /proc/sys/vm/drop_caches
-bash: /proc/sys/vm/drop_caches: Permission denied
You will get permission denied as the redirection will be performed as the user calling sudo, not as the superuser. So if you don't have permission to write to the target file, you will get permission denied.
To solve the problem, use the following method
sudo sh -c 'echo 1 > /proc/sys/vm/drop_caches'
Run tasks in parallel with xargs
Answer:
xargs provided a very simple to parallel tasks, e.g. setting P=3 means run 3 processes in parallel
seq 1 10 | xargs -n 1 -P 3 echo
Result:
1
2
3
4
5
7
6
9
8
10
Try to run the command several times, you might notice that number's order might be changed.
Why? Since they are running in parallel and some numbers finished first and some later!
