Have you ever wondered how much seconds passed since 00:00:00 Jan 1 1970 (unix time)?
OK, here goes the answer…
date -d \”May 31 21:15:00 2003\” +%s
or
date -d now +%s
Archive for May, 2003
Converting normal time to Unix time
Saturday, May 31st, 2003umount: /mnt/XXXX: device is busy
Monday, May 12th, 2003Are your tired of those nasty messages telling you can’t umount /mnt/cdrom?
Well here goes a little trick…
lsof | grep /mnt/cdrom
This will output the process(es) that are using the device. Now stop or kill the process and you are done.
There are another approach to this question, but let’s see if you have ideas on this…
More security for your files and directories
Monday, May 12th, 2003There is a tool called chattr that allows you to change/set file attributes on a GNU/Linux second extended (ext2) filesystem.
For example to protect myfile.txt, proceed as follows…
chattr +i myfile.txt
A file with the “i” (immutable) attribute cannot be modified: it cannot be deleted or renamed, no link can be created to this file and no data can be written to the file. Only the superuser or a process pessessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
Cleaning up core files
Sunday, May 11th, 2003When an application crashes, the kernel saves the state of the process in a core file for later analysis. This will help to determine the cause of a failure.
To avoid your hard disk being populated by unnecessary core files, you can seek and destroy those files older than 4 days:
find / -name core -atime +4 -exec rm -f \”{}\” ‘;’
To make your life easier you should add the above line to a cron job.
Tunneling over OpenSSH
Sunday, May 11th, 2003One of the beauties of the OpenSSH suite tools is that you can connect to remote host from your localhost by creating a secure connection through both ends.
Let’s say you want to “tunnel” mail from your laptop to your remote mail server…
ssh -l user -L 110:mailhost:110 -N mailhost
Specifies that the given port on the local host is to be forwarded to the given host and port on the remote side (-L).
The -l switch specifies a login name and -N avoids the execution of a remote command.
Using GnuPG
Saturday, May 10th, 2003GnuPG is the GNU Privacy Guard, the open source equivalent to Pretty Good Privacy (PGP). You can use GnuPG to encrypt and/or sign your mails or files and hence transmit them in a more secure fashion and ensure their integrity.
There are graphical environments to handle GnuPG but here we are going to use text-based commands.
First of all me must generate a key pair:
gpg –gen-key
The first time you run this command it will create some directories and files, so you need to launch the command again to create the keyrings.
When prompted select these options:
DSA and ElGamal
Keysize 1024
Expire time 0 (never expires)
Personal info
Passphrase
For the moment accepting default values is fine. Be careful with your passphrase as it will be used to encrypt/decrypt and sign your data, so do not simply choose the first silly words you guess 
Once you have your key-pairs, you are ready to start using GnuPG.
gpg -ea -r karkoma myfile.txt
Encrypts myfile.txt using karkoma’s public key with an ASCII armor (more on this in my next article).
gpg -d myfile.txt.asc >myfile.txt
Decrypts myfile.txt.asc (enter your passphrase)
gpg –clearsign -a myfile.txt
Signs myfile.txt. Once signed, the smallest modification to the file will indicate an invalid signature.
gpg –verify myfile.txt.asc
Verifies your file signature.
gpg -ba myfile.tar.gz
Signs a binary file
That’s all folks, just for now. I am preparing a more complete article regarding GnuPG, so come back soon.
