I am using 2.91
I am rendering a scene (remotely/ssh) with the following command
blender -b new.blend -E CYCLES -f 1 -o //frame_ -F PNG -x 1 -- --cycles-device CPU
I did not find the rendered image relative to my blend file, instead I see the following output. It appears to be that the render output option is not used by blender, it still write the image to the /tmp directory instead of next to my blend file.
Fra:1 Mem:49.06M (Peak 49.60M) | Time:00:27.91 | Remaining:00:00.00 | Mem:1.84M, Peak:2.24M | Scene, View Layer | Rendered 509/510 Tiles, Sample 128/128
Fra:1 Mem:48.95M (Peak 49.60M) | Time:00:27.92 | Mem:1.73M, Peak:2.24M | Scene, View Layer | Rendered 510/510 Tiles
Fra:1 Mem:48.95M (Peak 49.60M) | Time:00:27.92 | Mem:1.73M, Peak:2.24M | Scene, View Layer | Finished
Fra:1 Mem:47.11M (Peak 49.60M) | Time:00:27.92 | Sce: Scene Ve:0 Fa:0 La:0
Saved: '/tmp/0001.png'
Time: 00:28.52 (Saving: 00:00.60)
Blender quit