[Android Q&A, Help & Troubleshooting] gintama_me:
I have tried from TWRP, not sure I had no mistake so this is my account of my actions

Went to TWRP and tried flash Magisk-v18.1.zip

Got error of inability mounting /system https://imgur.com/Xb17FxF

Went and mount /system manually https://imgur.com/oOfNQiw

Went to a terminal and enter the command https://imgur.com/DielQsU

this is a log

__bionic_open_tzdata: couldn't find any tzdata when looking for Europe/Kiev!

__bionic_open_tzdata: couldn't find any tzdata when looking for GMT!

__bionic_open_tzdata: couldn't find any tzdata when looking for posixrules!

Starting TWRP 2.8.7.0 on Wed May 1 08:15:42 2019

(pid 2656)

I:=> hardware id from cpuinfo: 'M76'

I:=> serial from cpuinfo: '0000000000000000'

TW_NO_REBOOT_BOOTLOADER := true

RECOVERY_SDCARD_ON_DATA := true

TW_ALWAYS_RMRF := true

I:Lun file '/sys/devices/platform/usb_mass_storage/lun0/file' does not exist, USB storage mode disabled

I:Found brightness file at '/sys/devices/ti_lm3697_i2c.8/i2c-5/5-0036/backlight/lm3697_bl/brightness'

I:TWFunc::Set_Brightness: Setting brightness control to 1680

Starting the UI...Pixel format: 1536x2560 @ 32bpp

Pixel format: BGR_565

Not using qualcomm overlay, ''

framebuffer: fd 3 (1536 x 2560)

I:Scaling the curtain width 1.422222x and height 1.333333x

=> Linking mtab

Renaming regular /etc/recovery.fstab -> /etc/recovery.fstab.bak

Moving /etc/twrp.fstab -> /etc/recovery.fstab

=> Processing recovery.fstab

I:Processing '/system'

I:Processing '/cache'

I:Processing '/data'

I:Unable to unmount '/data'

I:Setting up '/data' as data/media emulated storage.

E:Unable to unmount '/data'

I:Backup folder set to '/data/media/0/TWRP/BACKUPS/0000000000000000'

I:Settings storage is '/data/media/0'

Updating partition details...

E:Unable to mount '/system'

I:Actual block device: '/dev/block/mmcblk0p41', current file system: 'ext4'

I:Data backup size is 1690MB, free: 2508MB.

...done

I:Unmounting main partitions...

Partition Logs:

/system | /dev/block/mmcblk0p41 | Size: 0MB Used: 0MB Free: 0MB Backup Size: 0MB

Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_Available_in_GUI IsPresent

Primary_Block_Device: /dev/block/mmcblk0p41

Display_Name: System

Storage_Name: System

Backup_Path: /system

Backup_Name: system

Backup_Display_Name: System

Storage_Path: /system

Current_File_System: ext4

Fstab_File_System: ext4

Backup_Method: files

/cache | /dev/block/mmcblk0p43 | Size: 247MB Used: 0MB Free: 247MB Backup Size: 0MB

Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_During_Factory_Reset Wipe_Available_in_GUI IsPresent

Primary_Block_Device: /dev/block/mmcblk0p43

Display_Name: Cache

Storage_Name: Cache

Backup_Path: /cache

Backup_Name: cache

Backup_Display_Name: Cache

Storage_Path: /cache

Current_File_System: ext4

Fstab_File_System: ext4

Backup_Method: files

/data | /dev/block/mmcblk0p44 | Size: 26719MB Used: 1690MB Free: 2508MB Backup Size: 1690MB

Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_During_Factory_Reset Wipe_Available_in_GUI IsPresent Has_Data_Media Can_Encrypt_Backup Use_Userdata_Encryption Is_Storage Is_Settings_Storage

Symlink_Path: /data/media/0

Symlink_Mount_Point: /sdcard

Primary_Block_Device: /dev/block/mmcblk0p44

Display_Name: Data

Storage_Name: Internal Storage

Backup_Path: /data

Backup_Name: data

Backup_Display_Name: Data

Storage_Path: /data/media/0

Current_File_System: ext4

Fstab_File_System: ext4

Backup_Method: files

MTP_Storage_ID: 65537

I:Loading package: TWRP (/script/ui.xml)

I:Load XML directly

I:Loading package: TWRP (/data/media/0/TWRP/theme/ui.zip)

I:Loading zip theme

I:Loading package: TWRP (/twres/ui.xml)

I:Load XML directly

I:Checking resolution...

I:Scaling theme width 1.422222x and height 1.333333x, offsets x: 0 y: 0

I:Loading resources...

open_png /twres/images/logo.png

open_png /twres/images/main_button.png

open_png /twres/images/main_button_half_height.png

open_png /twres/images/main_button_half_height_full_width.png

open_png /twres/images/fab_selectfolder.png

open_png /twres/images/tab_3.png

open_png /twres/images/tab_4.png

open_png /twres/images/file.png

open_png /twres/images/folder.png

open_png /twres/images/unlock_icon.png

open_png /twres/images/home.png

open_png /twres/images/back.png

open_png /twres/images/console.png

open_png /twres/images/checkbox_false.png

open_png /twres/images/checkbox_true.png

open_png /twres/images/radio_false.png

open_png /twres/images/radio_true.png

open_png /twres/images/sort_asc.png

open_png /twres/images/sort_desc.png

open_png /twres/images/sort_empty.png

open_png /twres/images/indeterminate001.png

open_png /twres/images/indeterminate002.png

open_png /twres/images/indeterminate003.png

open_png /twres/images/indeterminate004.png

open_png /twres/images/indeterminate005.png

open_png /twres/images/indeterminate006.png

open_png /twres/images/indeterminate007.png

open_png /twres/images/indeterminate008.png

open_png /twres/images/indeterminate009.png

open_png /twres/images/indeterminate010.png

open_png /twres/images/indeterminate011.png

open_png /twres/images/indeterminate012.png

open_png /twres/images/indeterminate013.png

open_png /twres/images/progress_empty.png

open_png /twres/images/progress_fill.png

open_png /twres/images/slider.png

open_png /twres/images/slider_used.png

open_png /twres/images/slider_touch.png

open_png /twres/images/handle.png

open_png /twres/images/cursor.png

open_png /twres/images/backspace.png

open_png /twres/images/enter.png

open_png /twres/images/shift.png

open_png /twres/images/shift_fill.png

open_png /twres/images/space.png

I:Loading variables...

I:Loading mouse cursor...

I:Loading pages...

I:PageSet::CheckInclude loading filename: '/twres/portrait.xml'

I:Loading included resources...

I:Loading included variables...

I:Loading mouse cursor...

I:Loading included pages...

I:Loading page main

I:Loading page main2

I:Loading page install

I:Loading page flash_confirm

I:Loading page flash_zip

I:Loading page flash_done

I:Loading page flashimage_confirm

I:Loading page clear_vars

I:Loading page confirm_action

I:Loading page action_page

I:Loading page singleaction_page

I:Loading page action_complete

I:Loading page filecheck

I:Loading page rebootcheck

I:Loading page wipe

I:Loading page advancedwipe

I:Loading page formatdata

I:Loading page formatdata_confirm

I:Loading page checkpartitionlist

I:Loading page partitionoptions

I:Loading page refreshfilesystem

I:Loading page selectfilesystem

I:Loading page backup

I:Loading page backup_options

I:Loading page backupname1

I:Loading page backupname2

I:Loading page backupencryption

I:Loading page backupencryption2

I:Loading page checkbackuppassword

I:Loading page backup_run

I:Loading page restore

I:Unable to open '/data/media/0/TWRP/BACKUPS/0000000000000000'

I:Loading page restore_read

I:Loading page restore_decrypt

I:Loading page try_restore_decrypt

I:Loading page restore_select

I:Loading page renamebackup

I:Loading page restore_run

I:Loading page mount

I:Loading page usb_mount

I:Loading page usb_umount

I:Loading page system_readonly_check

I:Loading page reboot

I:Loading page system_readonly

I:Loading page settings

I:Loading page settings_timezone

I:Loading page settings_screen

I:Loading page settings_vibration

I:Loading page advanced

I:Loading page partsdcard

I:Loading page htcdumlock

I:Loading page lock

I:Loading page filemanagerlist

I:Loading page filemanageroptions

I:Loading page choosedestinationfolder

I:Loading page filemanagerrenamefile

I:Loading page filemanagerrenamefolder

I:Loading page filemanagerchmod

I:Loading page filemanagerconfirm

I:Loading page filemanageraction

I:Loading page decrypt

I:Loading page decrypt_pattern

I:Loading page trydecrypt

I:Loading page terminalfolder

I:Loading page terminalcommand

I:Loading page sideload

I:Loading page fixperms

I:Loading page installsu

I:Loading page slideout

I:Loading page select_storage

I:Set page: 'clear_vars'

I:Set page: 'main2'

I:Switching packages (TWRP)

SELinux contexts loaded from /file_contexts

Full SELinux support is present.

I:Not using /misc, not defined in fstab.

I:Not using /misc, not defined in fstab.

Startup Commands:

ro.sf.lcd_density=640

ro.adb.secure=1

ro.cmd.WORLD_PHONE=true

ro.com.android.dateformat=MM-dd-yyyy

ro.nfc.platform=nxppn547

ro.soc.vendor=SAMSUNG

ro.arch=exynos5430

ro.hwui.fbo_cache_size=30

ro.hwui.path_cache_size=37

ro.hwui.layer_cache_size=60

ro.hwui.texture_cache_size=80

ro.hwui.disable_asset_atlas=true

ro.hwui.gradient_cache_size=4

ro.hwui.r_buffer_cache_size=9

ro.hwui.use_gpu_pixel_buffer=false

ro.hwui.drop_shadow_cache_size=8

ro.hwui.text_large_cache_width=2048

ro.hwui.text_small_cache_width=1024

ro.hwui.text_large_cache_height=1024

ro.hwui.text_small_cache_height=1024

ro.hwui.texture_cache_flushrate=0.4

ro.twrp.boot=1

ro.twrp.version=2.8.7.0

ro.wifi.channels=

ro.allow.mock.location=0

ro.board.platform=exynos5

ro.build.id=LMY48W

ro.build.cta=noncta

ro.build.args=

ro.build.date=Wed Jan 4 17:38:40 CST 2017

ro.build.date.utc=1483522720

ro.build.host=mz-builder-8

ro.build.mask.id=5.1.1-1483521401_intlstable

ro.build.tags=release-keys

ro.build.type=user

ro.build.user=flyme

ro.build.flavor=meizu_m76-user

ro.build.inside.id=5.1.1-20170104171641

ro.build.display.id=Flyme 5.1.12.1G

ro.build.product=mx4pro

ro.build.version.sdk=22

ro.build.version.release=5.1.1

ro.build.version.codename=REL

ro.build.version.incremental=1483522655

ro.build.version.all_codenames=REL

ro.build.description=meizu_mx4pro-user 5.1.1 LMY48W 1483522655 release-keys

ro.build.fingerprint=Meizu/meizu_mx4pro/mx4pro:5.1.1/LMY48W/1483522655:user/release-keys

ro.build.characteristics=phone

ro.flyme.published=true

ro.meizu.sip.support=true

ro.meizu.voip.support=false

ro.meizu.region.enable=true

ro.meizu.secure.version=0

ro.meizu.carrier.model=M462

ro.meizu.product.model=M462

ro.meizu.hardware.psn=76116B00JJJC

ro.meizu.hardware.soc=EXYNOS5430

ro.meizu.hardware.hifi=true

ro.meizu.hardware.support=0x7

ro.meizu.hardware.version=M462_intl_official

ro.meizu.security=false

ro.meizu.customize.pccw=false

ro.meizu.published.type=prd

ro.meizu.contactmsg.auth=false

ro.meizu.setupwizard.flyme=true

ro.meizu.setupwizard.setlang=true

ro.meizu.autorecorder=true

ro.meizu.permanentkey=false

ro.meizu.visualvoicemail=true

ro.radio.noril=0

ro.config.ringtone=03_Flyme.ogg

ro.config.mms_sound=01_Triumph.ogg

ro.config.alarm_alert=19_Waltz.ogg

ro.config.email_sound=02_Reminder.ogg

ro.config.calendar_sound=03_Doorbell.ogg

ro.config.notification_sound=02_Reminder.ogg

ro.crypto.state=unencrypted

ro.crypto.fuse_sdcard=true

ro.dalvik.vm.native.bridge=0

ro.secure=1

ro.zygote=zygote32

ro.carrier=unknown

ro.product.cpu.abi=armeabi-v7a

ro.product.cpu.abi2=armeabi

ro.product.cpu.abilist=armeabi-v7a,armeabi

ro.product.cpu.abilist32=armeabi-v7a,armeabi

ro.product.cpu.abilist64=

ro.product.name=meizu_mx4pro

ro.product.perf.config=M76-l1_base

ro.product.board=mx4pro

ro.product.brand=Meizu

ro.product.model=MX4 Pro

ro.product.cuptsm=MEIZU|ESE|01|02

ro.product.device=mx4pro

ro.product.locale.region=US

ro.product.locale.language=en

ro.product.mobile.name=m76

ro.product.manufacturer=Meizu

ro.baseband=unknown

ro.bootmode=unknown

ro.hardware=m76

ro.opengles.version=196609

ro.revision=0

ro.serialno=76OBCLB223ZT

ro.telephony.call_ring.multiple=false

ro.telephony.default_network=21

ro.bootloader=unknown

ro.debuggable=0

ro.factorytest=0

log.tag.VibeTonz=ERROR

net.bt.name=Android

net.tcp.default_init_rwnd=60

net.dns1=8.8.8.8

net.dns2=8.8.4.4

net.change=net.tcp.default_init_rwnd

sys.lte.mode=csfb

sys.usb.vid=2A45

sys.usb.bicr=no

sys.usb.state=mtp,adb

sys.usb.config=mtp,adb

sys.usb.charging=no

sys.lucid.powerxtend.version=353

sys.meizu.m35x.white.config=false

sys.meizu.white.config=false

sys.baseband=UMTS

init.svc.drm=restarting

init.svc.eeh=restarting

init.svc.adbd=running

init.svc.gpsd=restarting

init.svc.lmkd=restarting

init.svc.logd=restarting

init.svc.netd=stopped

init.svc.vold=restarting

init.svc.media=restarting

init.svc.flymed=running

init.svc.get_sn=stopped

init.svc.sdcard=restarting

init.svc.zygote=stopped

init.svc.console=restarting

init.svc.healthd=running

init.svc.ueventd=running

init.svc.fpdaemon=restarting

init.svc.immvibed=stopped

init.svc.installd=restarting

init.svc.keystore=restarting

init.svc.mobicore=restarting

init.svc.setup_fs=stopped

init.svc.debuggerd=restarting

init.svc.mcuupdate=stopped

init.svc.nvmserver=restarting

init.svc.watchdogd=running

init.svc.enableswap=stopped

init.svc.ril-daemon=restarting

init.svc.cploadserver=restarting

init.svc.flash_recovery=stopped

init.svc.servicemanager=restarting

init.svc.surfaceflinger=stopped

qemu.hw.mainkeys=1

twrp.crash_counter=0

vold.post_fs_data_done=1

wifi.interface=wlan0

debug.hwc.otf=1

debug.hwui.render_dirty_regions=true

dalvik.vm.isa.arm.features=div

dalvik.vm.heapsize=512m

dalvik.vm.dex2oat-Xms=64m

dalvik.vm.dex2oat-Xmx=512m

dalvik.vm.dexopt-flags=m=y

dalvik.vm.dex2oat-filter=speed

dalvik.vm.heapgrowthlimit=256m

dalvik.vm.stack-trace-file=/data/anr/traces.txt

dalvik.vm.image-dex2oat-Xms=64m

dalvik.vm.image-dex2oat-Xmx=64m

dalvik.vm.image-dex2oat-filter=speed

persist.sys.usb.config=mtp,adb

persist.sys.use.flyme.icon=true

persist.sys.meizu.region=cn

persist.sys.meizu.codepage=gbk

persist.sys.dalvik.vm.lib.2=libart.so

persist.sys.memopt.switch=1

persist.sys.country=US

persist.sys.current.cp=4

persist.sys.audience.selkw=0

persist.sys.audience.ustrhal=0

persist.sys.language=en

persist.sys.log-main.enable=0

persist.sys.timezone=Europe/Kiev

persist.sys.localevar=

persist.sys.log-radio.enable=0

persist.sys.log-events.enable=0

persist.sys.log-system.enable=0

persist.sys.strictmode.disable=true

persist.sys.profiler_ms=0

persist.sys.en_tc_partflush=false

persist.sys.log_reject_level=3

persist.sys.static_blur_mode=false

persist.sys.disable_blur_view=true

persist.sys.alloc_fc_as_needed=true

persist.sys.keyguard_intercept=true

persist.call.waiting.volume=45

persist.demo.hdmirotationlock=false

persist.dtmf.volume=75

persist.hdmi.hdcp_enabled=0

persist.perf.wm_static_blur=true

persist.radio.auto.switch=1

persist.radio.error.tdnvm=0

persist.radio.oriented.operator=1

persist.radio.simswitch=1

persist.radio.simswitch.iccid=N/A

persist.dialpad.ecc.volume=45

persist.dialpad.volume=45

persist.service.adb.enable=

persist.service.bdroid.bdaddr=22:22:eb:f8:50:34

selinux.reload_policy=1

service.mrvl.eeh.version=0.2

service.mrvl.cpload.version=0.3

service.mrvl.nvmserver.version=0.3

keyguard.no_require_sim=true

supolicy.loaded=1

I:Copying file /cache/recovery/log to /cache/recovery/last_log

tw_get_context got selinux context: u:object_r:media_rw_data_file:s0

I:Got default contexts and file mode for storage files.

I:Attempt to load settings from settings file...

I:Loading settings from '/data/media/0/TWRP/.twrps'.

I:Backup folder set to '/data/media/0/TWRP/BACKUPS/0000000000000000'

I:Copying file /etc/recovery.fstab to /cache/recovery/recovery.fstab

I:Version number saved to '/cache/recovery/.version'

__bionic_open_tzdata: couldn't find any tzdata when looking for WET-2WET,M3.5.0,M10.5.0!

__bionic_open_tzdata: couldn't find any tzdata when looking for posixrules!

I:TWFunc::Set_Brightness: Setting brightness control to 1680

I:Enabling MTP during startup

I:Starting MTP

Starting MTP

I:Get_Max_FileSize::maxFileSize: 17592186044416

I:sending message to add 65537 '/data/media/0' 'Internal Storage'

I:Message sent, add storage ID: 65537

MTP Enabled

I:Unable to mount '/system'

I:Actual block device: '/dev/block/mmcblk0p41', current file system: 'ext4'

I:Check_Lifetime_Writes failed to mount '/system'

I:Switching packages (TWRP)

created new mtpserver object

MtpServer::run fd: 20

mtppipe add storage 65537 '/data/media/0'

MtpStorage id: 65537 path: /data/media/0

I:Set page: 'install'

I:Set page: 'flash_confirm'

I:Set page: 'flash_zip'

I:operation_start: 'Flashing'

Installing '/data/media/0/1/Magisk-v18.1.zip'...

Checking for MD5 file...

Skipping MD5 check: no MD5 file found

I:Zip does not contain SELinux file_contexts file in its root.

I:Legacy property environment initialized.

1038+1 records in

1038+1 records out

1063528 bytes (1.0MB) copied, 0.013101 seconds, 77.4MB/s

Archive: /data/media/0/1/Magisk-v18.1.zip

inflating: META-INF/com/google/android/update-binary

inflating: META-INF/com/google/android/updater-script

inflating: arm/magiskboot

inflating: arm/magiskinit

inflating: chromeos/futility

inflating: chromeos/kernel.keyblock

inflating: chromeos/kernel_data_key.vbprivk

inflating: common/addon.d.sh

inflating: common/boot_patch.sh

inflating: common/magisk.apk

inflating: common/util_functions.sh

inflating: x86/magiskboot

inflating: x86/magiskinit

inflating: META-INF/MANIFEST.MF

inflating: META-INF/CERT.SF

inflating: META-INF/CERT.RSA

************************

* Magisk v18.1 Installer

************************

- Mounting /system, /vendor

mount: mounting /dev/block/mmcblk0p41 on /system failed: Device or resource busy

! Cannot mount /system

- Unmounting partitions

I:Legacy property environment disabled.

E:Error executing updater binary in zip '/data/media/0/1/Magisk-v18.1.zip'

Error flashing zip '/data/media/0/1/Magisk-v18.1.zip'

Updating partition details...

I:Data backup size is 1690MB, free: 2508MB.

...done

I:Set page: 'flash_done'

I:operation_end - status=1

I:Set page: 'clear_vars'

I:Set page: 'install'

I:Set page: 'main'

I:Set page: 'clear_vars'

I:Set page: 'main2'

I:Set page: 'mount'

I:Set page: 'main'

I:Set page: 'clear_vars'

I:Set page: 'main2'

I:Set page: 'install'

I:Set page: 'flash_confirm'

I:Set page: 'flash_zip'

I:operation_start: 'Flashing'

Installing '/data/media/0/1/Magisk-v18.1.zip'...

Checking for MD5 file...

Skipping MD5 check: no MD5 file found

I:Zip does not contain SELinux file_contexts file in its root.

I:Legacy property environment initialized.

1038+1 records in

1038+1 records out

1063528 bytes (1.0MB) copied, 0.018904 seconds, 53.7MB/s

Archive: /data/media/0/1/Magisk-v18.1.zip

inflating: META-INF/com/google/android/update-binary

inflating: META-INF/com/google/android/updater-script

inflating: arm/magiskboot

inflating: arm/magiskinit

inflating: chromeos/futility

inflating: chromeos/kernel.keyblock

inflating: chromeos/kernel_data_key.vbprivk

inflating: common/addon.d.sh

inflating: common/boot_patch.sh

inflating: common/magisk.apk

inflating: common/util_functions.sh

inflating: x86/magiskboot

inflating: x86/magiskinit

inflating: META-INF/MANIFEST.MF

inflating: META-INF/CERT.SF

inflating: META-INF/CERT.RSA

************************

* Magisk v18.1 Installer

************************

- Mounting /system, /vendor

- Target image: /dev/block/mmcblk0p23

- Device platform: arm

- Removing system installed root

- Constructing environment

Invalid image: not signed

- Unpacking boot image

MagiskBoot v18.1(18100) (by topjohnwu) - Boot Image Modification Tool

Parsing boot image: [/dev/block/mmcblk0p23]

No boot image magic found!

! Unable to unpack boot image

- Unmounting partitions

I:Legacy property environment disabled.

E:Error executing updater binary in zip '/data/media/0/1/Magisk-v18.1.zip'

Error flashing zip '/data/media/0/1/Magisk-v18.1.zip'

Updating partition details...

I:Data backup size is 1694MB, free: 2503MB.

...done

I:Set page: 'flash_done'

I:operation_end - status=1

I:Set page: 'clear_vars'

I:Set page: 'main2'

I:Set page: 'advanced'

I:Set page: 'filemanagerlist'

I:Set page: 'main'

I:Set page: 'clear_vars'

I:Set page: 'main2'

I:Set page: 'advanced'

I:Set page: 'confirm_action'

I:Set page: 'action_page'

I:operation_start: 'Copy Log'

I:Copying file /tmp/recovery.log to /data/media/0/recovery.log