grab_vcsa(1)

💖 grab_vcsa — Linux console vcsa grabber 💖

okay so bestie, welcome to grab_vcsa(1), the little setuid icon that gets you access to your console's video buffer. this is the Linux console vcsa grabber and she is very specific about her job. let's get into it 🫶

✨ NAME ✨

grab_vcsa — Linux console vcsa grabber

🌸 SYNOPSIS 🌸

grab_vcsa

no arguments, no flags, no drama. she just does the thing 💅

🦋 DESCRIPTION 🦋

so here's the lore. The Linux console allows text mode video buffer access^. For each tty device (/dev/tty0..31) there exist two devices (/dev/vcs0..31) and (/dev/vcsa0..31). These devices are two different representations of the content of the console. two whole vibes, same console content, iykyk ✨

now the annoying part. When you login on the Linux console, your tty device is changed owner to you, so you can read/write it. When you logout it is takes from you. and like... that's cute and all, but This does not happen with the vcs and vcsa devices, i.e. you cannot access the video buffer of your own tty. literally not your own tty. the audacity 😭

Unfortunately there is a lot of reason to use the text mode video buffer. For instance, it is not possible to get access to the full 256 characters the VGA adapter can display without using the text mode video buffer (Linux emulates the vt100 character set which does not have all VGA characters). This annoyance severely limits the porting possibilities to Linux of software that was written with a VGA character set in mind. like, 256 characters vs. a vt100 subset? not the same, bestie, not even close 💀

enter our main character. grab_vcsa is a setuid root program that, when called will change the owner of the vcs and vcsa devices to you, after a series of security checks have been performed. she does her homework first, then she hands over the keys 👑

and no, It is not necessary to change the permissions back again (this would be pointless since a user could kill a imaginary release_vcsa program before it can do its work). The permissions are automatically reverted on logout. so don't stress about cleanup, the system handles it, periodt 💖

also a fun fact for the lore girlies: grab_vcsa is used by the Free Pascal video unit. The video unit allows programmers to develop portable programs across Dos, Linux, FreeBSD, Windows, OS/2 and other operating systems while they can still assume being able to use the full VGA character set. cross-platform AND full VGA charset? she ate and left no crumbs 🌈

👑 RETURN CODES 👑

grab_vcsa has the following return codes:

• 0 — Success ✨ (she slayed)
• 1 — You are not running on the Linux console
• 2 — Error while statting tty.
• 3 — Error while executing chown.
• 4 — Error while executing chmod.
• 4 — You do not own your own tty.

yes bestie, 4 shows up twice in the original. not a typo on my end, that's just how it is. two very different problems, one shared number 🫠

🎀 AUTHOR 🎀

Daniel Mantione <daniel.mantione@freepascal.org>

🌟 a little sign-off 🌟

this whole thing comes to you courtesy of Free Pascal, dated 22 jan 2006, and it's page grab_vcsa(1) of the manual. go grab your vcsa, bestie, you've earned it 💅🎀✨