adb kill-server
adb connect <%TARGET_PC_IP_OR_HOSTNAME%>:<%EMULATOR_PORT%>
for emulator on my pc it was
adb kill-server
adb connect localhost:5555
Source: stackoverflow.com
adb kill-server
adb connect <%TARGET_PC_IP_OR_HOSTNAME%>:<%EMULATOR_PORT%>
adb kill-server
adb connect localhost:5555
$ adb devices
List of devices attached
???????????? no permissions
$ su
$ adb kill-server
$ adb start-server
$ adb devices
$ lsusb
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 044: ID 18d1:2d66 <- this is my mobile
Bus 002 Device 004: ID 0451:2046 Texas Instruments, Inc. TUSB2046 Hub
Bus 002 Device 003: ID 10d5:0001 Uni Class Technology Co., Ltd
$ su
$ vim /etc/udev/rules.d/51-android.rules
SUBSYSTEM=="usb", SYSFS{idVendor}=="18d1", MODE="0666"
SUBSYSTEM=="usb", SYSFS{idVendor}=="18d1", OWNER="%YOUR_USER%" GROUP="%YOUR_USER_GROUP%"