Hashing is one of the most useful practices a sysadmin can employ. I think too many sysadmins do not use this as a regular part of their everyday work. Even a home user on a windows box can utilize hashing to save yourself a lot of headache!
Quick tutorial how to get your MD5 and/or SHA-1 hash on linux, windows, and AIX
What is a hash?
First, if you do not know what an MD5 or SHA-1 hash is, check out my previous article:
Even if you do know what that means, check out the article anyway and see the various ways you can use this to your advantage. It is super awesome and very helpful, if I do say so myself!
How To Do MD5 and SHA-1 Hash Computation On….
- md5sum [filename]
- sha1sum [filename]
- csum -h MD5 [filename]
- csum -h SHA1 [filename]
- fciv -md5 [filename]
- fciv -sha1 [filename]
FCIV is a Microsoft utility and stands for “File Checksum Integrity Verifier”. You can download the install file here: Microsoft File Checksum Integrity Verifier. After installed, a utility fciv.exe will be extracted to a directory of your choosing
NOTE: I had previously mentioned using cygwin. Still very handy if you want a lot of linux/unix utilities on your Windows box. But for simple hashing, use Microsoft’s FCIV. Quick to install, quick to use
Examples of using hashing on linux, AIX, and Windows
So how does this help us as a computer user or a sysadmin?
In short, anytime you are copying files from one location to another (including download from internet) and want to verify the files are intact and pristine. Helpful when downloading from mirror site instead of original vendor site. Helpful when ftp’ing large files from one company location to another. And so on.
Here are some examples of me actually using hashing in my everyday job and everyday life
- Verify downloaded software is intact
- In place of recursive diff when comparing two directories
- Same as above, but now comparing directories on different servers
- What about if there’s no network access? And there are thousands of files
- Oracle export and import to copy a database from one server to another ..with NO network access!
- Finding new install media from non-official sources
For the full details of the above examples and ways I have saved myself a lot of sysadmin headaches utilizing hashing, go check out the previously mentioned blog post:
So yes, I still use hashing…all the time
For me specifically, IT’S AWESOME! Many of my uses are internal (like the Oracle import/export or the internal comparison of directories on servers with no network access).