Linux, programming and more
The simplest way to remove files older than $NUMBER of days..
Dry run (files will be NOT deleted, you will see a list with files older than 100 days)
1 | find -mtime +100 | less |
Another dry run, see what would be delete:
1 2 3 | find -mtime +600 | xargs echo rm rm /var/log/squid3/access.log.0 rm /var/log/squid3/access.log.2 |
Finally if you decided to remove the files – the final command to delete them:
1 | find -mtime +600 | xargs rm |
Maybe you know this problem, if more than one user has root access to a server you have very little chances to control who was it. The only hook could be date and time. Default if you issue the “history” command you see a command number and the operation.
Put the next line in your .bashrc and you will see date and time in your history:
1 2 | # Bash Timestamps export HISTTIMEFORMAT="%F %T " |
Finely to make it work execute:
1 | source .bashrc |
Your new history format:
1 2 3 4 5 | 536 2011-05-31 22:06:44 less /var/log/syslog 537 2011-05-31 22:06:46 ll 538 2011-05-31 22:06:54 vim rssh.pl 539 2011-05-31 22:07:07 perl rssh.pl 540 2011-05-31 22:07:16 ss -lnp |
I think you now this problem, you have a lot different hosts with different ssh ports.
It takes to much time to write the full ssh commands and recognize all of your ports:
Easy solution – use aliases:
1 2 3 4 5 6 | vim .ssh/config # Add this Host piper HostName piper User root Port 1022 |
1 | ssh piper |
root@web2:$ rm pe-warn-*.bz2
-bash: /bin/rm: Argument list too long
This peoblem happens when you are trying to delete too many files in a directory at the same time – it seems rm has special limits …
To solve the problem:
Use:
1 | find . -name 'pe-warn-*.bz2' | xargs rm |
or
1 | find . -name "pe-warn-*.bz2" -delete |
I remember being very confused for a very long time about the trailing garbage in commands that I saw in Linux systems.
Now I can explain it to you with a very easy example.
Standard in, out, and error
There are 3 standard sources of input and output for a program. Standard input usually comes from the keyboard if it’s an interactive program, or from another program if it’s processing the other program’s output. The program usually prints to standard output, and sometimes prints to standard error. These three file descriptors (you can think of them as “data pipes”) are often called STDIN, STDOUT and STDERR
Sometimes they’re not named, they’re numbered! The built-in numberings for them are 0, 1, and 2, in that order. By default, if you don’t name or number one explicitly, you’re talking about STDOUT.
Given that context, you can see the command above is redirecting standard output into /dev/null, which is a place you can dump anything you don’t want (often called the bit-bucket), then redirecting standard error into standard output (you have to put an & in front of the destination when you do this).
Will create a new directory
1 | mkdir test |
if you execute it second time you will get a error.
With this redirection you will suppress the error.
1 | mkdir test > /dev/null 2>&1 |
The short explanation, therefore, is “all output from this command should be shoved into a black hole.” That’s one good way to make a program be really quiet! That means, if you have some critical errors in your code, you will never see them.