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 reverse print a file?
Answer:
Normally, you can print a file to standard out by using
cat test.txt
It will show something like:
a
b
c
However, if you want to start from the last line, you can use tac (actually it is reverse of the cat command)
tac test.txt
It will give:
c
b
a
Delete files older than x days in Linux?
Answer:
For example, to delete files under /tmp folder, which were modified more than 6 days, use the command
find /tmp -mtime +5 | xargs rm
How to perform simple calculations in Linux shell?
Answer:
Use the "bc" commad.
echo "101+1" | bc
It will gives:
102
How to check the current logrotate status?
Answer:
logrotate will maintain a status file, normally at the location /var/lib/logrotate/status , you can view the content of this file to see the latest status of all log files managed by logrotate.
Example:
logrotate state -- version 2
"/var/log/apache2/access.log" 2008-12-7
"/var/log/apache2/error.log" 2009-1-25
...
Therefore, it is useful to verify if your desired log files are controlled by logrotate or not.
How to mirror a directory to a remote server over SSH?
Answer:
You can use rsync command for this purpose
Assume you want to mirror the local folder "/home/john" to remote server 192.168.1.5, under the folder "/data/backup/", you need to use the following command
rsync -avuz -e ssh /home/john 192.168.1.5:/data/backup/
If you want to dry-run the rsync, use the "n" flag, e.g.
rsync -avuzn -e ssh /home/john 192.168.1.5:/data/backup/
For more options, checkout the rsync document: http://www.samba.org/ftp/rsync/rsync.html
