# FAQ
The FAQ, Frequently Asked Questions, page contains **technical solutions** for common problems concerning the installation of Kerberos. This page does **NOT** contain non-technical questions and answers; The Raspberry Pi doesn't turn on, I don't have WIFI access, etc. Therefore you can access our [**knowledge base**](https://kerberosio.zendesk.com).
* [How to access the Raspberry Pi](#how-to-access-the-pi)
* [How to expand SD card root partition](#expand-sd-card)
* [Arch Linux](#expand-sd-card-archlinux)
* [How to backup SD card](#backup-sd-card)
* [How to setup WIFI connection on Raspberry Pi](#setup-wifi)
* [How to enable Raspberry Pi Camera Module](#how-to-enable-camera-module)
* [Arch Linux](#how-to-enable-camera-module-archlinux)
* [Clean up disk and memory space](#clean-up-disk)
## How to access the Raspberry Pi
Kerberos is built on Arch Linux, which by default is installed **without** a **Graphical User Interface**. This means that when attaching the Raspberry Pi to a monitor or connecting with SSH, will **only show you a command prompt**.
macbook:~ cedricverstraeten$ ssh root@ 192.168.0.10
root@ 192.168.0.10's password:
You can sign in with the default Arch Linux credentials: username "**root**" and password "**root**".
## How to expand SD card root partition
### Arch Linux (Raspberry Pi A, B, B+)
After logging in you view the status of filesystem (the output can be different):
[root@alarmpi build]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 1.7G 1.6G 0 100% /
devtmpfs 214M 0 214M 0% /dev
tmpfs 218M 0 218M 0% /dev/shm
tmpfs 218M 312K 218M 1% /run
tmpfs 218M 0 218M 0% /sys/fs/cgroup
tmpfs 218M 0 218M 0% /tmp
/dev/mmcblk0p1 90M 27M 64M 30% /boot
tmpfs 44M 0 44M 0% /run/user/0
Using the command fdisk will edit the filesystem /dev/mmcblk0:
[root@alarmpi ~]# fdisk /dev/mmcblk0
Welcome to fdisk (util-linux 2.23.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help):
List the information and delete partition 2:
Command (m for help): p
Disk /dev/mmcblk0: 7.2 GiB, 7746879488 bytes, 15130624 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x417ee54b
Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 2048 186367 184320 90M c W95 FAT32 (LBA)
/dev/mmcblk0p2 186368 3667967 3481600 1.7G 5 Extended
/dev/mmcblk0p5 188416 3667967 3479552 1.7G 83 Linux
Command (m for help): d
Partition number (1,2,5, default 5): 5
Partition 5 has been deleted.
Command (m for help):
Command (m for help): d
Partition number (1,2,5, default 5): 2
Partition 2 has been deleted.
Command (m for help):
Create a new extended partition a logical volume:
Command (m for help): n
Partition type:
p primary (1 primary, 0 extended, 3 free)
e extended
Select (default p): e
Partition number (2-4, default 2): 2
First sector (186368-15564799, default 186368): (press enter)
Using default value 186368
Last sector, +sectors or +size(186368 - 15564799, default 15564799): (press enter)
Using default value 15564799
Partition 2 of type Extended and of size 7.3 GiB is set
Command (m for help): n
Partition type:
p primary (1 primary, 1 extended, 2 free)
l logical (numbered from 5)
Select (default p): l
Adding logical partition 5
First sector (188416-15564799, default 188416):
Using default value 188416
Last sector, +sectors or +(188416-15564799, default 15564799):
Using default value 15564799
Partition 5 of type Linux and of size 7.3 GiB is set
Check whether top block starts in the same place as the original (start)
Command (m for help): p
Disk /dev/mmcblk0: 7969 MB, 7969177600 bytes, 15564800 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x00057540
Device Boot Start End Blocks Id System
/dev/mmcblk0p1 2048 186367 92160 c W95 FAT32 (LBA)
/dev/mmcblk0p2 186368 15564799 7689216 5 Extended
/dev/mmcblk0p5 188416 15564799 7688192 83 Linux
Command (m for help):
If it starts again (in this case on 186368 p2 a 188416 p5) write changes and reboot.
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
[root@alarmpi ~]# reboot
After booting the system we online enlarge root partitions
[root@alarmpi ~]# resize2fs /dev/mmcblk0p5
resize2fs 1.42.8 (20-Jun-2013)
Filesystem at /dev/mmcblk0p5 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
The filesystem on /dev/mmcblk0p5 is now 1922048 blocks long.
Check and it is done :-)
[root@alarmpi ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 7.3G 447M 6.5G 7% /
devtmpfs 83M 0 83M 0% /dev
tmpfs 231M 0 231M 0% /dev/shm
tmpfs 231M 236K 231M 1% /run
tmpfs 231M 0 231M 0% /sys/fs/cgroup
tmpfs 231M 0 231M 0% /tmp
/dev/mmcblk0p1 90M 24M 67M 27% /boot
### Arch Linux (Raspberry Pi 2)
After logging in you view the status of filesystem (the output can be different):
[root@alarmpi ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 3.2G 2.8G 161M 95% /
devtmpfs 427M 0 427M 0% /dev
tmpfs 431M 0 431M 0% /dev/shm
tmpfs 431M 392K 431M 1% /run
tmpfs 431M 0 431M 0% /sys/fs/cgroup
tmpfs 431M 0 431M 0% /tmp
/dev/mmcblk0p1 100M 18M 83M 18% /boot
tmpfs 87M 0 87M 0% /run/user/0
Using the command fdisk will edit the filesystem /dev/mmcblk0:
[root@alarmpi ~]# fdisk /dev/mmcblk0
Welcome to fdisk (util-linux 2.23.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help):
List the information and delete partition 2:
Command (m for help): p
Disk /dev/mmcblk0: 7.2 GiB, 7746879488 bytes, 15130624 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x4bce3dec
Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 2048 206847 204800 100M c W95 FAT32 (LBA)
/dev/mmcblk0p2 206848 7000000 6793153 3.2G 83 Linux
Command (m for help): d
Partition number (1,2,5, default 5): 2
Partition 2 has been deleted.
Command (m for help):
Create a new extended partition a logical volume:
Command (m for help): n
Partition type:
p primary (1 primary, 0 extended, 3 free)
e extended
Select (default p): p
Partition number (2-4, default 2):
First sector (206848-15130623, default 206848):
Last sector, +sectors or +size{K,M,G,T,P} (206848-15130623, default 15130623):
Created a new partition 2 of type 'Linux' and of size 7.1 GiB.
Check whether top block starts in the same place as the original (start)
Command (m for help): p
Disk /dev/mmcblk0: 7.2 GiB, 7746879488 bytes, 15130624 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x4bce3dec
Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 2048 206847 204800 100M c W95 FAT32 (LBA)
/dev/mmcblk0p2 206848 15130623 14923776 7.1G 83 Linux
Command (m for help):
If it starts again (in this case on 186368 p2 a 188416 p5) write changes and reboot.
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
[root@alarmpi ~]# reboot
After booting the system we online enlarge root partitions
[root@alarmpi ~]# resize2fs /dev/mmcblk0p2
resize2fs 1.42.12 (29-Aug-2014)
Filesystem at /dev/mmcblk0p2 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
The filesystem on /dev/mmcblk0p2 is now 1865472 (4k) blocks long.
Check and it is done :-)
[root@alarmpi ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 7.0G 2.8G 3.9G 43% /
devtmpfs 427M 0 427M 0% /dev
tmpfs 431M 0 431M 0% /dev/shm
tmpfs 431M 392K 431M 1% /run
tmpfs 431M 0 431M 0% /sys/fs/cgroup
tmpfs 431M 0 431M 0% /tmp
/dev/mmcblk0p1 100M 18M 83M 18% /boot
tmpfs 87M 0 87M 0% /run/user/0
## How to backup SD card
You can backup your SD card, by typing following command in your terminal. This can be helpful, if you want to restore it later; for example when your SD card is broken.
sudo dd if=/dev/disk2 of=~/Desktop/kerberos-io.img bs=1m
## How to setup WIFI connection
### Installed Kerberos.io from image
When kerberos is installed with the image, you can edit the wireless.conf file on the SD card. Insert the SD card in your workstation and open the file **wireless.conf**. You will see a similar config like below, edit the ESSID property with the name of your WIFI connection and the property Key with the WIFI password.
Description='A simple WPA encrypted wireless connection'
Interface=wlan0
Connection=wireless
Security=wpa
ESSID='network-name'
Key='plain-text-password'
IP=static
Address='192.168.0.x/24'
Gateway='192.168.0.1'
DNS=('192.168.0.1')
# Uncomment this if your ssid is hidden
#Hidden=yes
### Installed Kerberos.io from source
#### Archlinux
We will use the netctl tool for this. First copy the wireless-wpa example from the examples directory to the boot directory.
cp /etc/netctl/examples/wireless-wpa /boot/wireless.conf
Make a symbol link to the netctl homedirectory and activate the netctl profile, so the WIFI connection will be made on boot up.
ln -s /boot/wireless.conf /etc/netctl/wlan
systemctl enable netctl-auto @wlan0.service
Edit the **/boot/wireless.conf** file with your WIFI credentials, please note that moving the wireless.conf to the /boot directory also makes us possible to change the credentials directly from the SD card itself. So you don't need to turn on the Raspberry Pi if you want to change the credentials.
The last step is to disable power management: edit the config file,
nano /etc/modprobe.d/8192cu.conf
and copy-paste the line below.
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0
Arch Linux shows strange behaviour when enabling WLAN. For some reason, cron will be triggered every minute and will consume a lot of CPU power. This problem has something to do with the timeserver ntpd. A simple fix to avoid this issue is to install the fake hardware clock. First you will need to install fake-hwclock.
pacman -S fake-hwclock
Enable fake-hwclock on startup.
systemctl enable fake-hwclock fake-hwclock-save.timer
systemctl start fake-hwclock
Install timeserver client
pacman -S ntp
Enable ntp on startup
systemctl enable ntpd.service
## How to enable Raspberry Pi Camera Module
### Arch Linux
To enable the camera module, you will need to add these lines to your /boot/config.txt. Note that this is already done when you've installed Kerberos by transferring image.
gpu_mem=128
start_file=start_x.elf
fixup_file=fixup_x.dat
disable_camera_led=1
## Clean up disk and memory space
The SD card of your Raspberry Pi, has limited space, therefore we need some process to clean up the images taken by the machinery.
mkdir /home/bash
nano /home/bash/run.sh
Copy paste the bash script
#!/bin/bash
################################################################
# Check if memory is more than 70%, if so refresh nodejs scripts
##
if [[ $(free | grep Mem | awk -F' ' '{ print $3/$2*100 }') > 70.0 ]];
then
/usr/bin/forever restartall ;
fi;
#############################################
# Only keep images of last 3 days on sd-card.
##
find /home/kerberos-web/public/capture/ -type f -name '*.jpg' -mtime +1 -exec rm {} \;
##############################################################
# Check if disk size is more than 95%, if so remove some files
# from the capture directory.
##
if [[ $(df -h | grep /dev/root | awk -F' ' '{ print $5/1 }' | tr ['%'] ["0"]) -gt 95 ]];
then
rm -f $( ls -d -1tr /home/kerberos-web/public/capture/* | head -n 500);
fi;
Give rights to bash script
chmod +x /home/bash/run.sh
chmod 755 /home/bash/run.sh
Start cronjob that will run this bash script
crontab -e
Add following line
*/10 * * * * /bin/sh /home/bash/run.sh