boot - Install Ubuntu from ISO... cannot install grub - Ask Ubuntu

i have broken ubuntu 14.04 lts system (i.e., not boot) in sda6 (in sda3, extended), booting 14.04 lts installation cd. sda6 readable, , can mount sda6, cannot boot. this additional info on cause of problems may help.

i mean install ubuntu 16.04.1 lts directly iso, new partition sda1 (primary). have placed iso file in directory in ext4 partition sda4 (primary). followed instructions in accepted answer of install ubuntu iso image directly hard disk of system running linux? . when try to

sudo update-grub

i get

/usr/bin/grub-probe: error: failed canonical path of '/cow'.

all references problem (failed canonical path of /cow , e.g.) indicate 1 should identify grub partition , perform couple of steps. not know if have such partition, nor how identify it. have 1 other partition sda2.

i guess in / volatile, , can have persistent stuff under mounted sda partitions.

here output of fdisk -l /dev/sda

disk /dev/sda: 750.2 gb, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors units = sectors of 1 * 512 = 512 bytes sector size (logical/physical): 512 bytes / 4096 bytes i/o size (minimum/optimal): 4096 bytes / 4096 bytes disk identifier: 0x7fa54200     device boot      start         end      blocks   id  system /dev/sda1       976564224  1078964223    51200000   83  linux /dev/sda2   *        2048     1955839      976896   83  linux /dev/sda3         1957886   976564223   487303169    5  extended partition 3 not start on physical sector boundary. /dev/sda4      1078964224  1465147391   193091584   83  linux /dev/sda5         1957888    66406399    32224256   82  linux swap / solaris /dev/sda6        66408448   976564223   455077888   83  linux  partition table entries not in disk order 

gparted shown below

i needed modify grub configuration boot iso image hd since bios changing usb boot password locked, linux live not viable.

i managed boot iso typing needed in grub editor @ boot time.

so, technically, solved problem without answering question, , still not know answer.

but installation failed anyway. got password bios, change boot usb, used linux live , installed 16.04 no problem.

conclusion: results of installation attempt iso on hd different usb, if should same (failure vs. success).