pi@raspberrypi:~ $ sudo usermod -aG i2c pi
pi@raspberrypi:~ $ cat /etc/modprobe.d/raspi-blacklist.conf
pi@raspberrypi:~ $ modprobe i2c_dev
pi@raspberrypi:~ $ lsmod
Module                  Size  Used by
cfg80211              427855  0
rfkill                 16037  1 cfg80211
snd_bcm2835            20511  0
snd_pcm                75698  1 snd_bcm2835
snd_timer              19160  1 snd_pcm
snd                    51844  3 snd_bcm2835,snd_timer,snd_pcm
bcm2835_gpiomem         3040  0
bcm2835_wdt             3225  0
uio_pdrv_genirq         3164  0
uio                     8000  1 uio_pdrv_genirq
w1_therm                3584  0
ds2482                  3580  0
wire                   25219  2 w1_therm,ds2482
cn                      4374  1 wire
i2c_dev                 5859  0
i2c_bcm2708             4770  0
ipv6                  347530  37
pi@raspberrypi:~ $ ls -l /dev/i2c-*
crw-rw---- 1 root i2c 89, 1 Jan 29 17:09 /dev/i2c-1
pi@raspberrypi:~ $ cat /boot/config.txt | grep dtparam
dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on
dtparam=audio=on
dtparam=spi=off
pi@raspberrypi:~ $ apt-get install i2c-tools
E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?
pi@raspberrypi:~ $ sudo apt-get install i2c-tools
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  libi2c-dev python-smbus
The following NEW packages will be installed:
  i2c-tools
0 upgraded, 1 newly installed, 0 to remove and 63 not upgraded.
Need to get 51.3 kB of archives.
After this operation, 227 kB of additional disk space will be used.
Get:1 http://archive.raspberrypi.org/debian/ jessie/main i2c-tools armhf 3.1.1+svn-2 [51.3 kB]
Fetched 51.3 kB in 0s (200 kB/s)
Selecting previously unselected package i2c-tools.
(Reading database ... 40810 files and directories currently installed.)
Preparing to unpack .../i2c-tools_3.1.1+svn-2_armhf.deb ...
Unpacking i2c-tools (3.1.1+svn-2) ...
Processing triggers for man-db (2.7.0.2-5) ...
Setting up i2c-tools (3.1.1+svn-2) ...
/run/udev or .udevdb or .udev presence implies active udev.  Aborting MAKEDEV invocation.
pi@raspberrypi:~ $ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
pi@raspberrypi:~ $ i2cdetect -l
i2c-1   i2c             3f804000.i2c                            I2C adapter
pi@raspberrypi:~ $ i2cget -y 1 0x18
Error: Could not set address to 0x18: Device or resource busy
pi@raspberrypi:~ $