$ cd ./tethered/cedric
$ ./initroot-tethered.sh
Welcome to initroot-cedric-tethered
...
(bootloader) <UTAG name="fsg-id" type="str" protected="false">
(bootloader)   <value>
(bootloader)     a initrd=0xA2100000,1588596
(bootloader)   </value>
(bootloader)   <description>
(bootloader)     FSG IDs, see http://goo.gl/gPmhU
(bootloader)   </description>
(bootloader) </UTAG>
OKAY [  0.015s]
finished. total time: 0.015s
target reported max download size of 536870912 bytes
sending 'aleph' (34319 KB)...
OKAY [  1.098s]
writing 'aleph'...
(bootloader) Invalid partition name aleph
FAILED (remote failure)
finished. total time: 1.101s
(bootloader) slot-count: not found
(bootloader) slot-suffixes: not found
(bootloader) slot-suffixes: not found
resuming boot...
OKAY [  0.006s]
finished. total time: 0.006s
uid=0(root) gid=0(root) groups=0(root),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3014(readproc) context=u:r:shell:s0
$ adb shell
cedric:/ # 

$ cd ./untethered/athene
$ ./initroot-untethered.sh 
Welcome to initroot-athene-untethered
Welcome to initroot-athene-tethered
...
(bootloader) <UTAG name="fsg-id" type="str" protected="false">
(bootloader)   <value>
(bootloader)     a initrd=0x92000000,2505052
(bootloader)   </value>
(bootloader)   <description>
(bootloader)     FSG IDs, see http://goo.gl/gPmhU
(bootloader)   </description>
(bootloader) </UTAG>

OKAY [  0.015s]
finished. total time: 0.015s
target reported max download size of 536870912 bytes
sending 'aleph' (35214 KB)...
OKAY [  1.131s]
writing 'aleph'...
(bootloader) Invalid partition name aleph
FAILED (remote failure)
finished. total time: 1.138s
(bootloader) slot-count: not found
(bootloader) slot-suffixes: not found
(bootloader) slot-suffixes: not found
resuming boot...
OKAY [  0.006s]
finished. total time: 0.006s
uid=0(root) gid=0(root) groups=0(root),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3014(readproc) context=u:r:kernel:s0
padC-initroot: 1 file pushed. 11.1 MB/s (22937600 bytes in 1.963s)
44800+0 records in
44800+0 records out
22937600 bytes transferred in 3.017 secs (7602784 bytes/sec)
...
(bootloader) <UTAG name="fsg-id" type="str" protected="false">
(bootloader)   <value>
(bootloader)     a rdinit= root=/dev/mmcblk0p41
(bootloader)   </value>
(bootloader)   <description>
(bootloader)     FSG IDs, see http://goo.gl/gPmhU
(bootloader)   </description>
(bootloader) </UTAG>

OKAY [  0.015s]
finished. total time: 0.015s
rebooting...

finished. total time: 0.815s
uid=0(root) gid=0(root) groups=0(root),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3014(readproc) context=u:r:kernel:s0
athene:/ # 

$ cd <initramfs folder>
$ find . | grep -v [.]$ | cpio -R root:root -o -H newc | gzip > ../initroot-<device>.cpio.gz
OR if padding is needed:
$ dd if=/dev/zero of=../pad ibs=1 count=<PAD_SIZE>
$ cp ../pad ../initroot-<device>.cpio.gz && find . | grep -v [.]$ | cpio -R root:root -o -H newc | gzip > ../tmp && ls -la ../tmp && cat ../tmp >> ../initroot-<device>.cpio.gz  && rm -fr ../tmp
$ cd ..

fastboot oem config fsg-id "a initrd=<SCRATCH_ADDR+PAD_SIZE>,<initroot.cpio.gz size-PAD_SIZE>"`
fastboot flash foo initroot-<device>.cpio.gz`
fastboot continue

$ adb shell
shamu:/ # id
uid=0(root) gid=0(root) groups=0(root),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3009(readproc) context=u:r:su:s0