so i Had a trouble booting into
download mode on my Samsung Galaxy J4 to boot twrprecovery.img and not flashing it after enabling "developers options" and "USB debugging" and "Unlock OEM" now bootloader is already unlocked under "Unlock OEM" I tried
adb devices it saw my phone I did
adb reboot bootloader it did not boot into bootloader so after a little research I found I had to use
adb reboot download I could enter download mode but when doing
fastboot devices with normal, sudo and su privileges it simply doesn't see it while in OS mode nor in the download mode. I tried booting into bootloader via recovery mode using poweroff+Vol up+Homescreen and then navigating to reboot to bootloader it simply reboots to the OS.
so why adb sees devices but not fastboot?
anonsam-X550CC ~ # uname -r 4.4.0-127-generic anonsam-X550CC ~ # cat /etc/os-release NAME="Linux Mint" VERSION="18.3 (Sylvia)" ID=linuxmint ID_LIKE=ubuntu PRETTY_NAME="Linux Mint 18.3" VERSION_ID="18.3" HOME_URL="http://www.linuxmint.com/" SUPPORT_URL="http://forums.linuxmint.com/" BUG_REPORT_URL="http://bugs.launchpad.net/linuxmint/" VERSION_CODENAME=sylvia UBUNTU_CODENAME=xenial Phone Model : SM-J400F/DS Baseband version : J400FXXU2ARI2 Build number : R16NW.J400FXXU2ARK2 Android version : 8.0.0 Android security patch level : November 1, 2018