[Android Q&A, Help & Troubleshooting] joelones:
Hello,

I have a relatively unknown phone: RIV R55 Reach Tech Xiamen.

I'd like to take a backup of at least /system /data prior to rooting using TWRP. I'm just not clear how to customize TWRP for the phone, basically how to map the partitions and change resolution. I think I can start from a Nexus 5 TWRP image and work from there. Can I simply mount the IMG and back the necessary changes to backup / restore? Or must I compile TWRP from scratch?

I was able to pull of some info: cat /proc/mounts

rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,relatime,mode=755,gid=1000 0 0
debugfs /mnt/debugfs debugfs rw,relatime,gid=512 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/platform/msm_sdcc.3/by-num/p17 /system ext4 ro,relatime,data=ordered 0 0
/dev/block/platform/msm_sdcc.3/by-num/p21 /data ext4 rw,nosuid,nodev,relatime,nomblk_io_submit,noauto_da_alloc,errors=panic,data=ordered 0 0
/dev/block/platform/msm_sdcc.3/by-num/p18 /cache ext4 rw,nosuid,nodev,relatime,data=ordered 0 0
/dev/block/platform/msm_sdcc.3/by-num/p15 /persist ext4 rw,nosuid,nodev,relatime,data=ordered 0 0
/dev/block/vold/179:20 /storage/sdcard0 vfat rw,nosuid,nodev,noexec,noatime,nodiratime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/vold/179:20 /mnt/secure/asec vfat rw,nosuid,nodev,noexec,noatime,nodiratime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
tmpfs /storage/sdcard0/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0
/dev/block/vold/179:33 /storage/sdcard1 vfat rw,nosuid,nodev,noexec,noatime,nodiratime,uid=1000,gid=1023,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

ls /dev/block/platform/msm_sdcc.1

lrwxrwxrwx root root 2015-02-02 10:57 mmcblk1 -> /dev/block/mmcblk1
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk1p1 -> /dev/block/mmcblk1p1

ls /dev/block/platform/msm_sdcc.3

drwxr-xr-x root root 2015-02-02 10:57 by-num
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0 -> /dev/block/mmcblk0
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p1 -> /dev/block/mmcblk0p1
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p10 -> /dev/block/mmcblk0p10
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p11 -> /dev/block/mmcblk0p11
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p12 -> /dev/block/mmcblk0p12
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p13 -> /dev/block/mmcblk0p13
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p14 -> /dev/block/mmcblk0p14
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p15 -> /dev/block/mmcblk0p15
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p16 -> /dev/block/mmcblk0p16
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p17 -> /dev/block/mmcblk0p17
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p18 -> /dev/block/mmcblk0p18
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p19 -> /dev/block/mmcblk0p19
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p2 -> /dev/block/mmcblk0p2
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p20 -> /dev/block/mmcblk0p20
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p21 -> /dev/block/mmcblk0p21
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p22 -> /dev/block/mmcblk0p22
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p23 -> /dev/block/mmcblk0p23
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p3 -> /dev/block/mmcblk0p3
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p4 -> /dev/block/mmcblk0p4
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p5 -> /dev/block/mmcblk0p5
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p6 -> /dev/block/mmcblk0p6
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p7 -> /dev/block/mmcblk0p7
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p8 -> /dev/block/mmcblk0p8
lrwxrwxrwx root root 2015-02-02 10:57 mmcblk0p9 -> /dev/block/mmcblk0p9

Any help would be greatly appreciated. Thanks

EDIT: I'm able to extract a twrp nexus 5 base image. Can I just alter the fstab.hammerhead inside initrd.img file for my /system and /data partitions?