[root@nixos:~]# nix-env -iA nixos.virtualgl
installing 'virtualgl-2.5.2'
building '/nix/store/vqrhd5pdhq45pkcfsm4d255fc91srial-user-environment.drv'...
error: packages '/nix/store/yli9k63shss97dirzqcjwamg3r5kskm4-virtualgl-2.5.2/bin/glxinfo' and '/nix/store/nmlifbhldl44xpdqrhs3mig9bi4icl0n-glxinfo-8.3.0/bin/glxinfo' have the 
same priority 5; use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' to change the priority of one of the conflicting packages (0 being the highest priority)
builder for '/nix/store/vqrhd5pdhq45pkcfsm4d255fc91srial-user-environment.drv' failed with exit code 1
error: build of '/nix/store/vqrhd5pdhq45pkcfsm4d255fc91srial-user-environment.drv' failed

[root@nixos:~]#