fastboot flash recovery img never completes

My Nexus 10 stopped booting. It shows an open padlock on startup and the Google text in the middle. So I figured my son unlocked the bootloader somehow after creatively following instructions he found on youtube. I then tried to proceed to installing a fresh rom. Saw that CM has the "Manta" roms. I have handy the main rom: cm-13.0-20160820-SNAPSHOT-ZNH5YAO0J6-manta.zip. I found two recovery roms: twrp-2.8.7.0-manta.img and cm-13.0-20160820-SNAPSHOT-ZNH5YAO0J6-manta-recovery.img. I'm able to get fastboot to see my device, after doing the vol up+down / power thing. But then the command fastboot -w flash recovery cm-13.0-20160820-SNAPSHOT-ZNH5YAO0J6-manta-recovery.img never completes. Creating filesystem with parameters: Size: 29783752704 Block size: 4096 Blocks per group: 32768 Inodes per group: 8192 Inode size: 256 Journal blocks: 32768 Label: Blocks: 7271424 Block groups: 222 Reserved block group size: 1024 Created filesystem with 11/1818624 inodes and 158176/7271424 blocks Creating filesystem with parameters: Size: 553648128 Block size: 4096 Blocks per group: 32768 Inodes per group: 6768 Inode size: 256 Journal blocks: 2112 Label: Blocks: 135168 Block groups: 5 Reserved block group size: 39 Created filesystem with 11/33840 inodes and 4363/135168 blocks sending 'recovery' (7860 KB)... OKAY [ 0.932s] writing 'recovery'... That never finishes. The tablet shows, aside from the laying down Android picture and the info, a blue line: "FASTBOOT STATUS - flash:recovery". It never gets past this. I tried this with both the recovery img files I found. Anyone have any idea why my Nexus 10 can't seem to complete this fastboot recovery installation? I'm doing this using Xubuntu 15.04 btw, and I don't have Windows handy. I seriously hope it isn't a Linux limitation thing. adb has always worked great. Fastboot sees and interacts with the device, so, that part should be good I hope.