Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Meaning of 2>&1 in crontab
Answer:
It is quite common to find the following line in crontab
32 5 * * * root /project/cron.sh >> /dev/null 2>&1
The meaning of 2>&1 at the end of line means to redirect the standard error stream (stderr) to the standard out stream (stdout), and finally redirect everything to /dev/null.
It is commonly used in crontab definition so if a given command return too much warnings, it will not be logged anywhere in the system in order to reduce the storage requirements.
How to redirect error message to a file
Answer:
Assume you have some program/script that print to the standard error stream (i.e. stderr)
E.g. error.pl
print STDERR 'error';
You cannot redirect the error message just by basic file redirection, e.g.
perl error.pl > error.txt
Instead, you need to use 2>
perl error.pl 2> error.txt
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 replace a character for a new line in vi?
Answer:
You might have tried
:%s/,/\n/g
But it didn't work.
Try replacing with \r instead
:%s/,/\r/g
