Introduction

ARM processors are widely used on various devices, like smartphones, tablets and small computers/boards. The main advantages of the ARM processor are :

• Low power consumption
• Low cost
• Very small device form factor

For more informations about the ARM architecture, feel free to read the following links :

• Wikipedia page explaining the ARM architecture

• Fedora ARM wiki page

Why CentOS on ARMv7hl boards

A lot of people are interested in running Linux on such kind of cheap/small boards , as home server appliance, domestic controller, small vpn endpoint, etc (the list isn't exhaustive). While it exists a lot of distributions already providing support for such boards, someone already using CentOS 7 x86_64 for his servers/workstations/laptops will be probably interested in managing even such small armv7hl boards with the same tools. That's why the CentOS AltArch SIG decided to try to port the exiting code from CentOS 7 x86_64 to the armv7hl/armhfp platform.

Tested and supported Boards

1. Cubietruck

1.1. working

• serial console
• hdmi output
• ethernet
• selinux in enforcing mode (see selinux notes below)
• integrated wifi : be sure to run latest kernel, and then :

curl http://dl.cubieboard.org/public/Cubieboard/benn/firmware/ap6210/nvram_ap6210.txt > /lib/firmware/brcm/brcmfmac43362-sdio.txt
systemctl reboot

1.2. untested

2. Bananapi

2.1. working

• serial console
• hdmi output
• ethernet
• selinux in enforcing mode (see selinux notes below)

2.2. not working

• embedded 4 port switch (for the R1 model)

2.3. untested

3. RaspberryPI2

3.1. working

• hdmi output
• ethernet
• selinux in enforcing mode (see selinux notes below) (starting from released kernel 4.4.26+)

3.2. i2c

echo -e "dtparam=i2c1=on\ndtparam=i2c_arm=on" >> /boot/config.txt
echo -e "i2c-bcm2708\ni2c-dev" >> /etc/modules-load.d/i2c.conf
yum install -y i2c-tools
systemctl reboot

3.3. not working

3.4. untested

4. RaspberryPI3

4.1. working

• hdmi output
• ethernet
• Emdedded wifi (but see instructions in the /root/README file to download/install the required Broadcom firmware)
• selinux in enforcing mode (see selinux notes below) (starting from released kernel 4.4.26+)

4.2. i2c

see instructions for rpi2

4.3. not working

4.4. untested

Other armhfp boards

As we build a RootFS, chances are that you can still use it on your armhfp device. Problem is that we can't test all possible boards, but if your board supports vanilla/upstream kernel, and also uboot, you can apply the following procedure :

After you have unpacked the Cubietruck image (generic RootFS using also vanilla kernel) to your SD card, you just have to do one additional step.

Let's suppose you do this from your linux laptop and that your board is Bananapro :

export boardmodel="Bananapro"
export sdcard="/dev/mmcblk0"
cd /tmp
wget http://mirror.centos.org/altarch/7/extras/armhfp/Packages/uboot-images-armv7-2018.03-2.el7.noarch.rpm
rpm2cpio uboot-images-armv7-2018.03-2.el7.noarch.rpm|cpio -ivdm
dd if=./usr/share/${boardmodel}/u-boot-sunxi-with-spl.bin of=${sdcard} bs=1024 seek=8 conv=fsync,notrunc

FYI Here is a list of boards that have a uboot file for armhfp (from uboot-images-2016.09):

How to install CentOS Userland armv7hl

1. How to unpack the image for your board

The first thing to do is to download the appropriate image for your board. You need at least a 4Gb SD card

You can find those here (see [Supported Boards] section) : http://mirror.centos.org/altarch/7/isos/armhfp

Once you have downloaded the corresponding image for your board model, transfer it to your SD card:

xzcat CentOS-Userland-7-armv7hl-Minimal-$RELEASE-$MODEL.img.xz | sudo dd of=$/path/to/sd/card status=progress bs=4M
sudo sync

TIP: : the 'status=progress' parameter for dd exists in the version supplied with CentOS 7.2.1511. If you're running another version or another distribution, verify first that it's supported. That parameter isn't mandatory, but written here for convenience, to track the transfer rate status to the SD card. The 'bs=4M' parameter is also used for a faster transfer rate to the SD card, as most SD cards have an erase block size of 4MB||

Once the image is transferred, you can put the SD card in the dedicated slot for your arm device, and boot it up.

The default settings for the installed image are :

• root password : centos
• eth0 setting : dhcp
• selinux status : permissive or disabled (board/kernel specific, see [Supported Boards] section and your model)
• no ntp/chronyd setup

You can automatically set the correct time with the following commands :

yum install chrony
systemctl start chronyd

2. How to resize/expand the RootFS for the whole SD card

Depending on the SD card size you used, you probably want to expand the RootFS (/) to the maximum capacity of the underlying SD card. For your convenience, we've added the cloud-utils-growpart tool, packaged as rpm and also available through the Extras repository for armv7hl.

If you just want to use/expand the whole remaining capacity, just run (as root, or with sudo right) the following command :

/usr/local/bin/rootfs-expand

Your board will reboot, load kernel/initrd, expand the partition, resize it and reboot. Once done, you'll be using your whole SD card.

3. SElinux status

Depending on your board model, the kernel used in the image can or not support selinux. See then first if that's the case (listed in the [Supported Boards] section)

Because of the way the images are generated on the buider machines, the selinux context isn't the correct one on the filesystem in those images. That's the reason why we decided to just have selinux configured in permissive mode (through /etc/sysconfig/selinux), but even started with selinux turned off (enforce=0 boot parameter)

If you want to switch to enforcing mode, you'll have so to first modify the following files

• /etc/sysconfig/selinux : change from "permissive" to "enforcing"
  • rpi2/rpi3 : /boot/cmdline.txt: change "enforce=0" to "enforcing=1"
  • other image/board[s]: /boot/extlinux/extlinux.conf : change the "enforce=0" to "enforce=1"

After that (and before rebooting ! ), be sure to issue the following command :

touch /.autorelabel

You can now reboot and the whole filesystem will get the correct selinux contexts applied

The relabel process can be really slow on such SD card : as an example, it can take up to 5 minutes on a cubietruck with a 4Gb SD card !

Interacting with the AltArch Arm32 group

1. Getting help

• Wiki release notes
• IRC : #centos-arm on freenode.net

2. Contributing to the Arm32 group

• IRC : #centos-arm on freenode.net

• Dedicated Arm-dev mailing list

• Willing to test armv7hl for specific packages ? or troubleshooting issues ? See the builders wiki page

FAQ

1. How can I update my kernel ?

Depending on which board image you're using, it can use the "generic" kernel or the raspberrypi variant. It's normally all configured automatically but even if you point to the correct repository, you'll have take care of the following (depending on the board variant):

1.1. raspberrypi 2 and 3

yum update will bring the updated kernel and nothing to be done, just reboot and you'll be using the new kernel

1.2. "generic" kernel

After yum will have installed the updated kernel, you'll still have to edit /boot/extlinux.conf to modify the kernel/initrd and then reboot. To help with that, there is now a update-boot script that you can call yourself. That tool will detect latest kernel that was installed and will update /boot/extlinux.conf. Worth noting that such /usr/bin/update-boot wrapper script was only added in centos-userland-release-7-3.1611.el7.centos.0.2.armv7hl, so be sure to at least have that pkg installed before trying to call update-boot.

2. How can I enable EPEL 7 on armhfp ?

The answer is easy in a sense that there is no official EPEL repository for armfhp. But because lot of users were asking for this, we decided to use the centos armhfp builders to (re)build Source packages from EPEL 7 (and try to track those automatically) when they're idle. Please note that it's just an automatic rebuild without any QA/test, and also resulting pkgs aren't signed either. To use that repository, proceed like this :

cat > /etc/yum.repos.d/epel.repo << EOF
[epel]
name=Epel rebuild for armhfp
baseurl=https://armv7.dev.centos.org/repodir/epel-pass-1/
enabled=1
gpgcheck=0

EOF