root@ubuntu:~ # /root/Desktop/legacy_142_linux/llxdoom
Apr 18 2004 Doom LEGACY v1.42 Birthday version 22:42:44
DOOM 2: Hell on Earth
Z_Init: Init zone memory allocation daemon.
system memory 187Mb free 2Mb
20 megabytes requested for Z_Init.
W_Init: Init WADfiles.
Added file /root/doom2.wad (2919 lumps)
Added file /root/legacy.dat (80 lumps)
This program is Free Software!
See the terms of the GNU General Public License
Using XFree86-VidModeExtension Version 2.2
Using MITSHM extension
X Error of failed request: BadColor (invalid Colormap parameter)
Major opcode of failed request: 1 (X_CreateWindow)
Resource id in failed request: 0x21
Serial number of failed request: 17
Current serial number in output stream: 20
You'll need to install the drivers for your video card. This Ubuntu wiki article should help:
Once that is done, make sure Load "glx" is in your X configuration file (/etc/X11/xorg.conf) and is not commented out with a #.
Also, it's generally a bad idea to run regular programs as root, or to even login as root at all. Use a regular user account and either su or sudo to temporarily get root privileges for programs that require it.
As a side note, try making your post subject more specific so that your question can be answered faster.