[Android Q&A, Help & Troubleshooting] bibikalka:
The old prompt ($) indicates that you have not gotten root. If this was root, you'd see this : (#).

Now, it is actually very easy to get root if you follow these instructions (in the very first post):

http://xdaforums.com/r1-hd/how-to/blu-r1-hd-v6-6-dirtycowed-f-amazon-root-t3490882

The issue with such a root shell is that it actually has very limited permissions, and so far it's not been possible to get around these limitations. Unfortunately, no dd access to the partitions we'd like to replace. See my session over here after app_process32 was Dirty Cow'ed (this root shell does not have any sign for the prompt, so just type in the commands) :

C:\Program Files\Minimal ADB and Fastboot>adb shell
shell@k6b:/ $ toybox nc localhost 11112
toybox nc localhost 11112
ciao

cd /data/local/tmp
cd /data/local/tmp

whoami
whoami
root

pwd
pwd
/data/local/tmp

cd ../test
cd ../test
ls
ls
toybox
sh
sh
lsh: Permission denied
> > > > > > > > > >

ls /dev/block
ls /dev/block
/dev/block: Permission denied
ls -l /dev/block
ls -l /dev/block
/dev/block: Permission denied

ls -l /etc
ls -l /etc
lrwxrwxrwx root root 2016-01-08 17:24 etc -> /system/etc

pwd
pwd
/data/local/test
dd if=/dev/zero of=dirtycow bs=1 count=13728
dd if=/dev/zero of=dirtycow bs=1 count=13728
13728+0 records in
13728+0 records out
13728 bytes transferred in 0.210 secs (65371 bytes/sec)
ls
ls
dirtycow
sec_config
toybox
ls -l
ls -l
-rw------- root root 13728 2016-01-09 10:48 dirtycow
-rw------- root root 6639 2016-01-09 10:37 sec_config
-rwxrwxrwx root root 258380 2016-01-08 13:55 toybox
chmod 0777 ./dirtycow
chmod 0777 ./dirtycow
./dirtycow
./dirtycow
lsh: Permission denied
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > ls -l
ls -l
-rwxrwxrwx root root 13728 2016-01-09 10:48 dirtycow
-rw------- root root 6639 2016-01-09 10:37 sec_config
-rwxrwxrwx root root 258380 2016-01-08 13:55 toybox
md5sum ./dirtycow
md5sum ./dirtycow
66d785b394f2a94229a1770c3b870563 ./dirtycow
./dirtycow
./dirtycow
lsh: Permission denied
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ls
ls
dirtycow
sec_config
toybox
whoami
whoami
root
getenforce
getenforce
Enforcing
reboot
reboot
usage reboot /default.prop /data/local/tmp/default.prop
ls
ls
dirtycow
sec_config
toybox

ls -l /cache
ls -l /cache
drwx------ system system 2015-12-31 19:01 backup
drwxrwxr-x system system 2015-12-31 19:00 encryption_log
drwxrwxr-x system system 2015-12-31 19:00 fota
drwxrwx--- root root 1969-12-31 19:00 lost+found
-rw------- root root 2655263 2016-01-03 12:12 ramdisk.gz
drwxrwx--- system cache 2015-12-31 19:01 recovery
ls -l /cache/recovery
ls -l /cache/recovery
-rw-r--r-- root root 0 2015-12-31 19:00 last_install
-rw------- system system 131654 2015-12-31 19:00 last_kmsg
-rw------- system system 135130 2015-12-31 19:00 last_kmsg.1
-rw-r--r-- system system 12149 2015-12-31 19:00 last_log
-rw-r--r-- system system 12122 2015-12-31 19:00 last_log.1
cp /cache/ramdisk.gz /local/bin/test
cp /cache/ramdisk.gz /local/bin/test
cp: /local/bin/test: No such file or directory
cp /cache/ramdisk.gz /data/local/test
cp /cache/ramdisk.gz /data/local/test
ls /data/local/test
ls /data/local/test
dirtycow
ramdisk.gz
sec_config
toybox
ls -l /data/local/test
ls -l /data/local/test
-rwxrwxrwx root root 13728 2016-01-09 10:48 dirtycow
-rw------- root root 2655263 2016-01-09 11:55 ramdisk.gz
-rw------- root root 6639 2016-01-09 10:37 sec_config
-rwxrwxrwx root root 258380 2016-01-08 13:55 toybox
chmod 0777 /data/local/test/ramdisk.gz
chmod 0777 /data/local/test/ramdisk.gz
chmod 0777 /data/local/test/sec_config
chmod 0777 /data/local/test/sec_config
ls /etc/install*
ls /etc/install*
/etc/install*: No such file or directory
ls /system/bin/install-recovery.sh
ls /system/bin/install-recovery.sh
/system/bin/install-recovery.sh: Permission denied
getcon
getcon
lsh: No such file or directory
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
> > > > > > > > > ls /dev/block/bootdevice
ls /dev/block/bootdevice
/dev/block/bootdevice
ls /dev/block/bootdevice/
ls /dev/block/bootdevice/
/dev/block/bootdevice/: Permission denied
ls /dev/block/bootdevice/by-name/
ls /dev/block/bootdevice/by-name/
/dev/block/bootdevice/by-name/: Permission denied
ls /dev/block/bootdevice/by-name/boot
ls /dev/block/bootdevice/by-name/boot
/dev/block/bootdevice/by-name/boot
ls -l /dev/block/bootdevice/by-name/boot
ls -l /dev/block/bootdevice/by-name/boot
lrwxrwxrwx root root 2016-01-08 17:24 boot -> /dev/block/mmcblk
0p36
ls -l /dev/block/bootdevice/by-name/boot
ls -l /dev/block/bootdevice/by-name/boot
lrwxrwxrwx root root 2016-01-08 17:24 boot -> /dev/block/mmcblk
0p36
ls -l /dev/block/bootdevice/by-name/laf
ls -l /dev/block/bootdevice/by-name/laf
lrwxrwxrwx root root 2016-01-08 17:24 laf -> /dev/block/mmcblk0
p35
cp /dev/block/bootdevice/by-name/laf /data/local/test
cp /dev/block/bootdevice/by-name/laf /data/local/test
cp: /dev/block/bootdevice/by-name/laf: Permission denied

ls /system/bin/net
ls /system/bin/net
/system/bin/net: No such file or directory
ls /system/bin/netd
ls /system/bin/netd
/system/bin/netd: Permission denied
ls -l /system/bin/netd
ls -l /system/bin/netd
/system/bin/netd: Permission denied
cat /proc/1/maps
cat /proc/1/maps
00008000-00096000 r-xp 00000000 00:01 3914 /init
00096000-00099000 r--p 0008d000 00:01 3914 /init
00099000-0009b000 rw-p 00090000 00:01 3914 /init
0009b000-00154000 rw-p 00000000 00:00 0 [heap]
b6f9c000-b6f9e000 rw-p 00000000 00:00 0
b6f9e000-b6fc2000 rw-s 00000000 00:0c 8283 /dev/__properties__
b6fc2000-b6fc3000 r--p 00000000 00:00 0
b6fc3000-b6fc4000 ---p 00000000 00:00 0
b6fc4000-b6fc6000 rw-p 00000000 00:00 0 [anon:thread signal stack]
b6fc6000-b6fc7000 r-xp 00000000 00:00 0 [sigpage]
becf0000-bed11000 rw-p 00000000 00:00 0 [stack]
ffff0000-ffff1000 r-xp 00000000 00:00 0 [vectors]

And so on ...