[HTC Sensation] lowiic:
I retrieved the recovery.log from 4ext for a ROM I tried to flash a couple of days ago, and I see a lot of "failed to" - "not such file or directory" - "read-only file system" - "unmount of /system failed" - ... So I put it here maybe it could help to understand the problem!

Starting recovery on Fri Jan 2 00:00:00 1970
can't open /dev/tty0: No such file or directory
framebuffer: fd 3 (540 x 960)

Welcome to 4EXT Recovery Touch

by madmaxx82

I:start load volumes..
Preparing boot.. 0 Preparing boot.. 0 Preparing boot.. 0 Preparing boot.. 0 Preparing boot.. 0 Preparing boot.. 1I:st.f_bsize: 4096
I:st.f_bsize: 4096
Preparing boot.. 1 Preparing boot.. 1recovery filesystem table
=========================
0 /tmp ramdisk (null) (null)
1 /recovery emmc /dev/block/mmcblk0p21 (null)
2 /boot emmc /dev/block/mmcblk0p20 (null)
3 /cache ext4 /dev/block/mmcblk0p24 (null)
4 /data ext4 /dev/block/mmcblk0p23 (null)
5 /sdcard vfat /dev/block/mmcblk1p1 /dev/block/mmcblk1
6 /system ext4 /dev/block/mmcblk0p22 (null)
7 /misc emmc /dev/block/mmcblk0p31 (null)

I:end load volumes..
I:Completed outputting fstab.
I:Processing arguments.
I:Checking arguments.
Command: "/sbin/recovery"

ro.build.date=Thu May 8 17:34:43 CEST 2014
ro.build.date.utc=0
ro.product.model=HTC Sensation
ro.product.brand=htc
ro.product.name=htc_pyramid
ro.product.device=pyramid
ro.product.board=pyramid
ro.product.cpu.abi=armeabi-v7a
ro.product.cpu.abi2=armeabi
ro.product.manufacturer=HTC
ro.product.locale.language=hdpi
ro.product.locale.region=
ro.board.platform=msm8660
ro.build.product=pyramid
ro.com.android.dateformat=MM-dd-yyyy
net.bt.name=Android
ro.serialno=SH1BTV809020
ro.baseband=11.24A.3504.31_M
ro.carrier=HTC-FRA
ro.bootloader=1.27.1100
ro.cid=HTC__203
ro.mid=PG5813000
init.svc.choice_fn=stopped
init.svc.htcbatt=running
init.svc.adbd=running
init.svc.recovery=running
ext.version="1006.2.0"
ext.feature.version_check=yes
ext.build=33
ext.edition=ng

I:preparing..
Preparing boot.. 1I:prep sys1: 0
Preparing boot.. 1 Preparing boot.. 2 Preparing boot.. 2 Preparing boot.. 2 Preparing boot.. 2 Preparing boot.. 2 Preparing boot.. 3 Preparing boot.. 3I:preparing.. fin
Preparing boot.. 3 Configuring settings..

Your configuration settings:

Using button backlights level: 90
4EXT SmartFlash: enabled
Restore: MD5Sum checks: enabled
Backups: generate MD5Sums: enabled
Backups: mode: tar
Backups: exclude /cache: disabled
Backups: exclude dalvik-cache: disabled
Preserve theme: enabled
Hide useless directories: disabled
Haptic feedback: enabled
Haptic feedback strength: 25
Timezone: configured
Using 24h-hour time format

I:theme propok
Recovery is ready..

I:have tz_data
I:Checking for extendedcommand...
I:Skipping execution of extendedcommand, file not found...

About to install:
Sensation_3.33.401.53_odexed.zip

Continue install?

-- Installing: /sdcard/Sensation_3.33.401.53_odexed.zip
Finding update package...
I:Update location: /sdcard/Sensation_3.33.401.53_odexed.zip
Opening update package...
Installing update...

unmount of /system failed; no such volume
Creating filesystem with parameters:
Size: 838859776
Block size: 4096
Blocks per group: 32768
Inodes per group: 7315
Inode size: 256
Journal blocks: 3200
Label:
Blocks: 204799
Block groups: 7
Reserved block group size: 55
Created filesystem with 11/51205 inodes and 6651/204799 blocks

===============================================
| Android Revolution HD |
| by mike1986 |
| Be patient - 1st boot may take a while |
===============================================

>>> Formatting partitions
(system is unmounted already)
Creating filesystem with parameters:
Size: 125787136
Block size: 4096
Blocks per group: 32768
Inodes per group: 7677
Inode size: 256
Journal blocks: 1024
Label:
Blocks: 30709
Block groups: 1
Reserved block group size: 7
Created filesystem with 11/7677 inodes and 1518/30709 blocks

>>> Mounting partitions

>>> Cleaning process

minzip: Extracted file "/system/app/AdobeReader.apk"
minzip: Extracted file "/system/app/AppSharing.apk"
minzip: Extracted file "/system/app/AppSharing.odex"
minzip: Extracted file "/system/app/ApplicationsProvider.apk"
minzip: Extracted file "/system/app/ApplicationsProvider.odex"
minzip: Extracted file "/system/app/BackupRestoreConfirmation.apk"
minzip: Extracted file "/system/app/BackupRestoreConfirmation.odex"
>>> Writing Data & System
minzip: Extracted file "/system/app/BlueSky.apk"
minzip: Extracted file "/system/app/Bluetooth.apk"
minzip: Extracted file "/system/app/Bluetooth.odex"
minzip: Extracted file "/system/app/BrcmBluetoothServices.apk"
minzip: Extracted file "/system/app/BrcmBluetoothServices.odex"
minzip: Error touching "/system/app/Browser.apk"

>>> Creating toolbox symlinks
symlink: failed to remove /system/bin/cat: Read-only file system
symlink: failed to symlink /system/bin/cat to toolbox: File exists
symlink: failed to remove /system/bin/chmod: Read-only file system
symlink: failed to symlink /system/bin/chmod to toolbox: File exists
symlink: failed to remove /system/bin/chown: Read-only file system
symlink: failed to symlink /system/bin/chown to toolbox: File exists
symlink: failed to remove /system/bin/cmp: Read-only file system
symlink: failed to symlink /system/bin/cmp to toolbox: File exists
symlink: failed to remove /system/bin/date: Read-only file system
symlink: failed to symlink /system/bin/date to toolbox: File exists
symlink: failed to remove /system/bin/dd: Read-only file system
symlink: failed to symlink /system/bin/dd to toolbox: File exists
symlink: failed to remove /system/bin/df: Read-only file system
symlink: failed to symlink /system/bin/df to toolbox: File exists
symlink: failed to remove /system/bin/dmesg: Read-only file system
symlink: failed to symlink /system/bin/dmesg to toolbox: File exists
symlink: failed to remove /system/bin/getevent: Read-only file system
symlink: failed to symlink /system/bin/getevent to toolbox: File exists
symlink: failed to remove /system/bin/getprop: Read-only file system
symlink: failed to symlink /system/bin/getprop to toolbox: File exists
symlink: failed to remove /system/bin/hd: Read-only file system
symlink: failed to symlink /system/bin/hd to toolbox: File exists
symlink: failed to remove /system/bin/id: Read-only file system
symlink: failed to symlink /system/bin/id to toolbox: File exists
symlink: failed to remove /system/bin/ifconfig: Read-only file system
symlink: failed to symlink /system/bin/ifconfig to toolbox: File exists
symlink: failed to remove /system/bin/iftop: Read-only file system
symlink: failed to symlink /system/bin/iftop to toolbox: File exists
symlink: failed to remove /system/bin/insmod: Read-only file system
symlink: failed to symlink /system/bin/insmod to toolbox: File exists
symlink: failed to remove /system/bin/ioctl: Read-only file system
symlink: failed to symlink /system/bin/ioctl to toolbox: File exists
symlink: failed to remove /system/bin/ionice: Read-only file system
symlink: failed to symlink /system/bin/ionice to toolbox: File exists
symlink: failed to remove /system/bin/kill: Read-only file system
symlink: failed to symlink /system/bin/kill to toolbox: File exists
symlink: failed to remove /system/bin/ln: Read-only file system
symlink: failed to symlink /system/bin/ln to toolbox: File exists
symlink: failed to remove /system/bin/log: Read-only file system
symlink: failed to symlink /system/bin/log to toolbox: File exists
symlink: failed to remove /system/bin/ls: Read-only file system
symlink: failed to symlink /system/bin/ls to toolbox: File exists
symlink: failed to remove /system/bin/lsmod: Read-only file system
symlink: failed to symlink /system/bin/lsmod to toolbox: File exists
symlink: failed to remove /system/bin/lsof: Read-only file system
symlink: failed to symlink /system/bin/lsof to toolbox: File exists
symlink: failed to remove /system/bin/mkdir: Read-only file system
symlink: failed to symlink /system/bin/mkdir to toolbox: File exists
symlink: failed to remove /system/bin/mount: Read-only file system
symlink: failed to symlink /system/bin/mount to toolbox: File exists
symlink: failed to remove /system/bin/mv: Read-only file system
symlink: failed to symlink /system/bin/mv to toolbox: File exists
symlink: failed to remove /system/bin/nandread: Read-only file system
symlink: failed to symlink /system/bin/nandread to toolbox: File exists
symlink: failed to remove /system/bin/netstat: Read-only file system
symlink: failed to symlink /system/bin/netstat to toolbox: File exists
symlink: failed to remove /system/bin/newfs_msdos: Read-only file system
symlink: failed to symlink /system/bin/newfs_msdos to toolbox: File exists
symlink: failed to remove /system/bin/notify: Read-only file system
symlink: failed to symlink /system/bin/notify to toolbox: File exists
symlink: failed to remove /system/bin/printenv: Read-only file system
symlink: failed to symlink /system/bin/printenv to toolbox: File exists
symlink: failed to remove /system/bin/ps: Read-only file system
symlink: failed to symlink /system/bin/ps to toolbox: File exists
symlink: failed to remove /system/bin/reboot: Read-only file system
symlink: failed to symlink /system/bin/reboot to toolbox: File exists
symlink: failed to remove /system/bin/renice: Read-only file system
symlink: failed to symlink /system/bin/renice to toolbox: File exists
symlink: failed to remove /system/bin/rm: Read-only file system
symlink: failed to symlink /system/bin/rm to toolbox: File exists
symlink: failed to remove /system/bin/rmdir: Read-only file system
symlink: failed to symlink /system/bin/rmdir to toolbox: File exists
symlink: failed to remove /system/bin/rmmod: Read-only file system
symlink: failed to symlink /system/bin/rmmod to toolbox: File exists
symlink: failed to remove /system/bin/route: Read-only file system
symlink: failed to symlink /system/bin/route to toolbox: File exists
symlink: failed to remove /system/bin/schedtop: Read-only file system
symlink: failed to symlink /system/bin/schedtop to toolbox: File exists
symlink: failed to remove /system/bin/sendevent: Read-only file system
symlink: failed to symlink /system/bin/sendevent to toolbox: File exists
symlink: failed to remove /system/bin/setconsole: Read-only file system
symlink: failed to symlink /system/bin/setconsole to toolbox: File exists
symlink: failed to remove /system/bin/setprop: Read-only file system
symlink: failed to symlink /system/bin/setprop to toolbox: File exists
symlink: failed to remove /system/bin/sleep: Read-only file system
symlink: failed to symlink /system/bin/sleep to toolbox: File exists
symlink: failed to remove /system/bin/smd: Read-only file system
symlink: failed to symlink /system/bin/smd to toolbox: File exists
symlink: failed to remove /system/bin/start: Read-only file system
symlink: failed to symlink /system/bin/start to toolbox: File exists
symlink: failed to remove /system/bin/stop: Read-only file system
symlink: failed to symlink /system/bin/stop to toolbox: File exists
symlink: failed to remove /system/bin/sync: Read-only file system
symlink: failed to symlink /system/bin/sync to toolbox: File exists
symlink: failed to remove /system/bin/top: Read-only file system
symlink: failed to symlink /system/bin/top to toolbox: File exists
symlink: failed to remove /system/bin/touch: Read-only file system
symlink: failed to symlink /system/bin/touch to toolbox: File exists
symlink: failed to remove /system/bin/umount: Read-only file system
symlink: failed to symlink /system/bin/umount to toolbox: File exists
symlink: failed to remove /system/bin/uptime: Read-only file system
symlink: failed to symlink /system/bin/uptime to toolbox: File exists
symlink: failed to remove /system/bin/vmstat: Read-only file system
symlink: failed to symlink /system/bin/vmstat to toolbox: File exists
symlink: failed to remove /system/bin/watchprops: Read-only file system
symlink: failed to symlink /system/bin/watchprops to toolbox: File exists
symlink: failed to remove /system/bin/wipe: Read-only file system
symlink: failed to symlink /system/bin/wipe to toolbox: File exists

symlink: failed to remove /system/bin/sh: Read-only file system
symlink: failed to symlink /system/bin/sh to /system/bin/mksh: File exists
symlink: failed to remove /system/fonts/DroidSans.ttf: Read-only file system
symlink: failed to symlink /system/fonts/DroidSans.ttf to /system/fonts/Roboto-Regular.ttf: File exists
symlink: failed to remove /system/fonts/DroidSans-Bold.ttf: Read-only file system
symlink: failed to symlink /system/fonts/DroidSans-Bold.ttf to /system/fonts/Roboto-Bold.ttf: File exists
symlink: failed to remove /system/vendor/firmware/hdcp.keys: Read-only file system
symlink: failed to symlink /system/vendor/firmware/hdcp.keys to /factory/hdcp.keys: Read-only file system
set_perm: chown of /system/bin/iptables to 0 1000 failed: Read-only file system
set_perm: chmod of /system/bin/iptables to 4750 failed: Read-only file system
set_perm: chown of /system/bin/netcfg to 0 3003 failed: Read-only file system
set_perm: chmod of /system/bin/netcfg to 2750 failed: Read-only file system
set_perm: chown of /system/bin/ping to 0 3004 failed: Read-only file system
set_perm: chmod of /system/bin/ping to 2755 failed: Read-only file system
set_perm: chown of /system/bin/reboot to 0 2000 failed: Read-only file system
set_perm: chmod of /system/bin/reboot to 6755 failed: Read-only file system
set_perm: chown of /system/bin/run-as to 0 2000 failed: Read-only file system
set_perm: chmod of /system/bin/run-as to 6750 failed: Read-only file system
set_perm: chown of /system/bin/tc to 0 1000 failed: Read-only file system
set_perm: chmod of /system/bin/tc to 4750 failed: Read-only file system
set_perm: chown of /system/etc/bluetooth to 0 0 failed: Read-only file system
set_perm: chmod of /system/etc/bluetooth to 755 failed: Read-only file system
set_perm: chown of /system/etc/bluetooth/a2dp_avrcp.conf to 0 0 failed: No such file or directory
set_perm: chmod of /system/etc/bluetooth/a2dp_avrcp.conf to 644 failed: No such file or directory
set_perm: chown of /system/etc/bluetooth/auto_pairing.conf to 1000 1000 failed: No such file or directory
set_perm: chmod of /system/etc/bluetooth/auto_pairing.conf to 640 failed: No such file or directory
set_perm: chown of /system/etc/bluetooth/blacklist.conf to 3002 3002 failed: No such file or directory
set_perm: chmod of /system/etc/bluetooth/blacklist.conf to 444 failed: No such file or directory
set_perm: chown of /system/etc/dbus.conf to 1002 1002 failed: No such file or directory
set_perm: chmod of /system/etc/dbus.conf to 440 failed: No such file or directory
set_perm: chown of /system/etc/dhcpcd/dhcpcd-run-hooks to 1014 2000 failed: Read-only file system
set_perm: chmod of /system/etc/dhcpcd/dhcpcd-run-hooks to 550 failed: Read-only file system
set_perm: chown of /system/etc/init.goldfish.sh to 0 2000 failed: No such file or directory
set_perm: chmod of /system/etc/init.goldfish.sh to 550 failed: No such file or directory
set_perm: chown of /system/etc/init.qcom.sdio.sh to 1000 1000 failed: No such file or directory
set_perm: chmod of /system/etc/init.qcom.sdio.sh to 555 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/left_eye-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/nose_base-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-r0-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-rn7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/multi_pose_face_landmark_detectors.3/right_eye-y0-yi45-p0-pi45-rp7-ri20.2d_n2/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-r0-ri30.4a/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-r0-ri30.4a/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-rn30-ri30.5/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-rn30-ri30.5/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-rp30-ri30.5/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/detection/yaw_roll_face_detectors.3/head-y0-yi45-p0-pi45-rp30-ri30.5/full_model.bin to 644 failed: No such file or directory
set_perm: chown of /system/vendor/pittpatt/models/recognition/face.face.y0-y0-22-b-N/full_model.bin to 0 0 failed: No such file or directory
set_perm: chmod of /system/vendor/pittpatt/models/recognition/face.face.y0-y0-22-b-N/full_model.bin to 644 failed: No such file or directory

>>> Creating additional symlinks

>>> Setting permissions

>>> Flashing boot.img

>>> Unmounting partitions
about to run program [/sbin/busybox] with 4 args