Cannot execute adb or fastboot

Even though you installed adt-bundle-sdk and jdk,
if you meet the below message after execution adb or fastboot on Ubuntu ,

bash: /home/user/android-sdk/sdk/platform-tools/adb: No such file or directory

You should install the below things,

sudo apt-get install libc6:i386 libncurses5:i386 libstdc++6:i386