Reseting NTFS ownership and attributes after a Windows reinstallation

Let's say you had to reinstal Windows 7, due to Microsoft having screwed so bad with its automatic update installer that it was the only option left. Now, you performed a semi-clean install, in that Windows installed a brand new copy, but moved the previous installation system directory into C:\Windows.old.

The usual problem, if you're using mutliple NTFS drives or partitions is that you may have files on these additional partitions that are owned by your previous account, which now has a completely different GUID than your new account. This means that you find that you have all the trouble in the world getting full access to files you rignfully own.

The solution?

In an elevated prompt, go to the additional drive and issue:
takeown /F * /R
icacls * /grant <your_user_name>:F /T
This will take a while, but it should reset ownerships and all these other pesky attributes that are a major annoyance to GETTING ANY WORK DONE!

Note that you can also try the following beforehand, if you want to reset all the access rights:
icacls * /T /Q /C /RESET

Securely erasing a drive in Linux

Now ain't that useful. From time to time you have to depart with an old disk, but of course, you're rather make sure it is properly erased of all its data before handing it off.

Well, what do you know, since 2001, nearly every HDD under the sun comes with a Secure Erase feature, as it is part of the ATA standard.

The even better news is that hdparm fully supports it (is there anything hdparm can't do?), thus, if you're on Linux and you need to securely erase all the data from a drive, all you need to do, say, if your disk is /dev/sdb, is:

# hdparm --user-master u --security-set-pass p /dev/sdb
security_password="p"

/dev/sdb:
 Issuing SECURITY_SET_PASS command, password="p", user=user, mode=high

# hdparm --user-master u --security-erase p /dev/sdb
security_password="p"

/dev/sdb:
 Issuing SECURITY_ERASE command, password="p", user=user

After a while, you should find that your drive has been securely erased. Neat!
Note that if you want to find out whether the security erase/enhanced erase feature is supported at all, as well as how long that erasing is going to take, you probably want to issue the following beforehand:

~# hdparm -I /dev/sdb

/dev/sdb:

ATA device, with non-removable media
        Model Number:       SAMSUNG HD322GJ
        Serial Number:      XXXXXXXXXXXXXX
        Firmware Revision:  XXXXXXXX
        Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6
(...)
Security:
        Master password revision code = 65534
                supported
        not     enabled
        not     locked
        not     frozen
        not     expired: security count
                supported: enhanced erase
        48min for SECURITY ERASE UNIT. 48min for ENHANCED SECURITY ERASE UNIT.

Setting passwords /etc/shadow

If you ever need to edit /etc/shadow to add an MD5 password manually (yes, this can happen for very legitimate reasons):

# openssl passwd -1 -salt abcd1234
Password: hunter1
$1$abcd1234$97fq4hZr.GzmcDQ5upZAX1

Also of reference: here and here