how to add custom resolution in fedora 25 ?

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Welcome to ask.fedora. 1440x900 sounds like a rather strange resolution; do you know what your aspect ratio is? Please run xrandr in a terminal and report the output in a comment. Speaking from recent experience, if your system isn't detecting a mode, it won't let you set it. (In my case, I suspect the graphics card, but let's not be hasty here.)

hi sideburns , I typed xrandr in the Terminal and this is the result :

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 1280 x 1024, maximum 1280 x 1024
default connected primary 1280x1024+0+0 0mm x 0mm
   1280x1024      0.00* 
   1024x768       0.00  
   800x600        0.00  
   640x480        0.00

Please note that in the past , Ubuntu was showing this resolution normally ,,,, I have tried many other debian-based distros like linux mint and tails , and There was no problem with the display .

Did you install from a LiveUSB? If so, boot from that and see if it detects your resolution correctly. I'm not sure where to go from there, but I am sure that somebody here knows.

the liveUSB doesn't show the correct resolution either !!

Can you either hook this monitor up to a different computer, or a different monitor on this one?