Xephyr :2 -host-cursor -screen 800x480x16 -dpi 96 -ac &

$ Initializing built-in extension Generic Event Extension
Initializing built-in extension SHAPE
Initializing built-in extension MIT-SHM
Initializing built-in extension XInputExtension
Initializing built-in extension XTEST
Initializing built-in extension BIG-REQUESTS
Initializing built-in extension SYNC
Initializing built-in extension XKEYBOARD
Initializing built-in extension XC-MISC
Initializing built-in extension SECURITY
Initializing built-in extension XINERAMA
Initializing built-in extension XFIXES
Initializing built-in extension RENDER
Initializing built-in extension RANDR
Initializing built-in extension COMPOSITE
Initializing built-in extension DAMAGE
Initializing built-in extension MIT-SCREEN-SAVER
Initializing built-in extension DOUBLE-BUFFER
Initializing built-in extension RECORD
Initializing built-in extension DPMS
Initializing built-in extension X-Resource
Initializing built-in extension XVideo
Initializing built-in extension XVideo-MotionCompensation
Initializing built-in extension SELinux
Initializing built-in extension GLX
(EE) 
(EE) Backtrace:
(EE) 0: Xephyr (xorg_backtrace+0x3d) [0x7fa5bd72a4bd]
(EE) 1: Xephyr (0x7fa5bd5a3000+0x18b229) [0x7fa5bd72e229]
(EE) 2: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7fa5bc5b5000+0xfbb0) [0x7fa5bc5c4bb0]
(EE) 3: /usr/lib/x86_64-linux-gnu/libpixman-1.so.0 (0x7fa5bca0f000+0x7153a) [0x7fa5bca8053a]
(EE) 4: /usr/lib/x86_64-linux-gnu/libpixman-1.so.0 (0x7fa5bca0f000+0x583bf) [0x7fa5bca673bf]
(EE) 5: /usr/lib/x86_64-linux-gnu/libpixman-1.so.0 (pixman_fill+0x31) [0x7fa5bca1a981]
(EE) 6: Xephyr (fbFill+0x300) [0x7fa5bd63c2d0]
(EE) 7: Xephyr (fbPolyFillRect+0x1a0) [0x7fa5bd653940]
(EE) 8: Xephyr (0x7fa5bd5a3000+0x13edac) [0x7fa5bd6e1dac]
(EE) 9: Xephyr (miPaintWindow+0x1d1) [0x7fa5bd6600a1]
(EE) 10: Xephyr (miWindowExposures+0x1d5) [0x7fa5bd660975]
(EE) 11: Xephyr (0x7fa5bd5a3000+0x94c2c) [0x7fa5bd637c2c]
(EE) 12: Xephyr (MapWindow+0x251) [0x7fa5bd627ed1]
(EE) 13: Xephyr (0x7fa5bd5a3000+0x330d0) [0x7fa5bd5d60d0]
(EE) 14: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xf5) [0x7fa5bad33de5]
(EE) 15: Xephyr (0x7fa5bd5a3000+0x3346f) [0x7fa5bd5d646f]
(EE) 
(EE) Segmentation fault at address 0x7fa5b8d8e000
(EE) 
Fatal server error:
(EE) Caught signal 11 (Segmentation fault). Server aborting
(EE)