Oracle Cloud has an always free tier, providing arm(aarch64) Ampere server with 24GB RAM and enough disk space to get you started. It provides significant value for customers. Does other cloud provider offer free tier compute services like this?

Google Cloud Platform (GCP)

Compute Engine: One e2-micro instance (0.25–0.5 vCPU, 1 GB RAM) per month in select regions (e.g., Iowa, Oregon, South Carolina), with 30 GB HDD and 1 GB egress.

Amazon Web Service (AWS)

No free VM, only free lambda service.

Microsoft Azure

One free VM for 1 year. After that no free VM, only limited function (serverless), container, static web app.

check kernel boot param

Check these two files

cat /proc/cmdline
cat /etc/default/grub

If ipv6.disable=1 is set, the kernel IPv6 stack will be disabled. If ipv6.disable_ipv6=1 is set, the kernel keeps the IPv6 stack functional but will not assign IPv6 addresses to any of your network devices.

Make sure you do not use any of these kernel options if you want to use IPv6.

check interface disable_ipv6 settings

sysctl net.ipv6.conf.lo.disable_ipv6
sysctl net.ipv6.conf.eno1.disable_ipv6
# -r list all values matching this pattern
sysctl -r 'net.ipv6.conf.*.disable_ipv6' net.ipv6.conf

Make sure all of the interfaces that you want to have ipv6 enabled has disable_ipv6=0. Specifically, you SHOULD also enable ipv6 on lo interface. You should also enable IPv6 on Linux bridge and the physical interface that it is connected to.

check interface RA settings if you use SLAAC

RA stands for router advertisement. It is a broadcast packet that allow configuration of IP address and routing. SLAAC relies on RA to work.

sysctl net.ipv6.conf.all.accept_ra
# replace vmbr0 with your interface
sysctl net.ipv6.conf.vmbr0.accept_ra

It should be 1 or 2 depending on your device.
If it’s 0, you need to set this at boot time. e.g. in /etc/network/interfaces

To learn more about accept_ra param, see Linux kernel document. Search accept_ra in that page.

For example, on one of my promox VE node, I have

auto vmbr0
iface vmbr0 inet static
        address 192.168.2.47/24
        gateway 192.168.2.1
        bridge-ports eno1
        bridge-stp off
        bridge-fd 0
iface vmbr0 inet6 auto
        accept_ra 2

If you doubt whether RA is working properly, run tcpdump to capture the packet and view it in wireshark.

# replace INTERFACE with your interface name
sudo tcpdump -i INTERFACE -w /tmp/ra_packets.pcap 'icmp6 and (ip6[40] = 134 or ip6[40] = 133)'

check lo ip6-loopback ping

ping6 ::1
ping6 ip6-loopback

check local hostname is ipv6 resolvable

in /etc/hosts
::1 entry should include your fqdn

check whether ipv6 address is assigned on interface

ip -6 a
ip -6 a vmbr0

If your IPv6 network use SLAAC, IP address should be assigned automatically. One interface usually has one public IPv6 address (starts with 2x:xx:xx) and more than one private IPv6 address (starts with fx:xx:xx).

If your IPv6 network use DHCPv6 only, you should config DHCP in /etc/network/interface or corresponding RHEL config file or Network Manager config file. To just test DHCPv6 is working, you can run:

dhclient -6 INTERFACE

check ipv6 routes is added

ip -6 r
ip -6 r | grep default

IPv6 routes are added by clients via RA (router advertisement).

Make sure the default route either has no expire field or has a good expire field. In openwrt default config, default route expire should be between 1200s and 1800s. If it’s less than 1200s, RA is not properly received and processed by host.

In some home server, if you enable IPv6 on IPMI/SBC/iLO/iDrac and use the shared network port, host OS will no longer receive the RA packet. You may see low expire on default route or missing a default route. In that case, you should disable IPv6 on IPMI.

check IPv6 neighbors for nodes in the same LAN

ip -6 n show|grep -v -E '(FAILED|STALE)'

At least one router should be listed when IPv6 is working. You can compare results on different nodes in the same LAN.

check you can visit other IPv6 nodes on the Internet

ping6 aliyun.com
curl -6 https://aliyun.com
curl -I -6 https://mirrors.tuna.tsinghua.edu.cn/
# test whether your OS prefer IPv6 or IPv4 when both are available
curl test.ipw.cn

You can’t toggle bluetooth on/off in GNOME applets.

rfkill list show bluetooth is not blocked.

bluetoothctl list show empty bluetooth controller list.

Solution

sudo modprobe -r btusb
sudo modprobe btusb

This will unload and reload btusb module, which may be able to fix the issue.

ref: [SOLVED] No bluetooth adaptater on AX200 / Kernel & Hardware / Arch Linux Forums

Here is how I use it:

Convert network speed. ISPs and network device use bit per second, downloaders usually use byte per second.

units 1000Mbps MiB/s
; 119.21 MiB/s
units 100Mbps MiB/s
; 11.92 MiB/s
units 20Mbps MiB/s
; 2.38 MiB/s
units 4Mbps KiB/s
; 488 KiB/s

Calculate average download speed

units 800MiB/25min KiB/s
; 546.1 KiB/s

Convert hard drive space. Operating systems show GiB/TiB, while vendors use GB/TB.

units 1TB GiB
; 931.3 GiB
units 2TB GiB
; 1862.6 GiB

You can do calculation too. For example, if you have 24 16TB disks. Each data is stored in 3 replicas. At 80% capacity, you may store up to

units 16TB*24/3*0.8 TiB
; 93.13 TiB

Do time calculations

units '2 hour + 34 min + 1 day'
; 95640 s
units '2 hour + 34 min + 1 day' hour
; 26.6 hour
units 8mo weeks
; 34.8 weeks

Convert between tps and maximum possible total request per day

units 132tps req/day
; 11404800 req/day
units 132tps million*req/day
; 11.4 million*req/day

Convert between (single node) tps and average response time

units 132tps ms/req
; 7.5 ms/req

Convert foreign currency to local currency

units 39.99hkd usd
; 5.1 usd

units 500hkd/mo usd/year
; 765 usd/year

You may have notice some units are not built-in. Units allow you to define your own units very easily. Here is my ~/.units file:

word    !
words   1 word

rmb     !
cny     rmb
RMB     rmb
hkd     0.9393 rmb
aud     4.6608 rmb
usd     7.2959 rmb
eur     8.266 rmb
euro    eur
gbp     9.7282 rmb
GBp     0.01gbp
jpy     0.050583 rmb
sgd     5.5781 rmb
s$      sgd
inr     0.081919 rmb
rs      inr
mvr     0.4637 rmb
laari   0.01 mvr

request !
req     request
r       request
tps     req/s

BTC     64219 usd
bitcoin 1 BTC
btc     BTC

ETH     3490 usd
Ether    1 ETH
Ethereum 1 ETH
eth      ETH

# units 0K tempC
# units 0K tempF

core    !

jin     0.5kg

char    !

share   !

w       10000
yi      100000000

tx      !
transaction   tx
trans   tx

kwh     1000*watt*hour

You can define basic unit by using ‘!’, you can define unit alias, you can define conversion. See man units for more information.

Of the choices in title, I have used Ubuntu, Debian and FreeBSD. I had evaluated Arch Linux and Gentoo to a great extend and decide not to use them. I have started to use Linux since around 2005. The first distros that got me interested in Linux was Red Hat Linux 9 and Fedora Core 4. I remember the days when I burned Fedora Core 4 and Ubuntu 6.10 CDs and gave them to others when I was in college. And Ubuntu sent free CDs with free shipping all over the world at that time.

Without further ado, let’s talk about features I care in Linux distro.

Stable Release Instead of Rolling Release

Actually rolling release means no release at all. In stable release, the kernel and package are tested, work together well and the feature set is frozen. Security or critical bug fix patches are provided without breaking backward compatibility. Stable release also means there is a documented process of upgrading old release to a new one. All backward incompatible changes are well documented.

Using a stable release doesn’t mean you have to stick with old versions of software. You can always compile the software you do want. For example, I used to compile mplayer and Emacs in Debian stable. Some software encourage you to use an official build, such as bugzilla. Some software have latest build maintained for Debian stable, such as postgresql. You are definitely not constrained by the software version that is in Debian stable’s apt repository. A stable release will make sure the underlying system and library is solid, if you want to get latest applications, go ahead. On the Linux desktop, AppImage and Flatpak is also becoming more popular. If you want to get OBS or DigiKam, there is a build for any Linux. Personally I still prefer OS native builds though.

If you want to learn more about how a stable release is made. Read Debian Release Management or FreeBSD’s release engineering. If you are a developer or project manager, you know making a good release is hard.

This rules out Arch Linux, which is a rolling release. Rolling release doesn’t mean install once and upgrade forever. It’s more like every package may break at every upgrade. You need to test software you use in a stage environment by yourself if you don’t want surprises. This also rules out Ubuntu non-LTS releases. I don’t call it a release anymore.

Binary Packages Instead of Source Packages

Unless you only use a fixed set of packages and rarely upgrade them, binary packages will greatly simplify and speed up software installation. Even if you have a fairly powerful machine, it still cause great pain if a low level library requires an update, which triggers a chain of recompiles. I was bitten by this once while I was using FreeBSD. For some dedicated web or database server, this may not be a big problem.

A side note for python developers. Since this year (2016), most PyPI packages are in wheel binary format, which makes installing faster and easier. It’s amazing that PyPI is developed and maintained by a single person.

This rules out Gentoo and FreeBSD ports.

Large Selection of Software and Large User Base

The core team should maintain a large selection of software, so if there are problems, they can be exposed and handled inside the project. Large user base means if you hit a problem, it’s likely there is already a fix or a workaround.

This rules out FreeBSD. Its binary package system is not as sophisticated as Debian’s. Binary packages and ports are not part of the official release.

Edit: In 2025, FreeBSD 14 offers significantly more binary packages than it did in 2016. If your hardware runs well on FreeBSD and you don’t need any Linux-only non-free software, you should give FreeBSD a try.

Worldwide Mirrors for Packages

This will speed up operating system install and upgrade, and package install greatly.

Honor Mentions About Other Distro

RedHat Enterprise Linux (RHEL)/Oracle Linux/Amazon Linux, Ubuntu LTS, OpenSUSE.

RHEL is very similar to Debian, if you prefer RedHat’s way of doing things, they are good choices. Also, RHEL has the best documentation between RHEL, Ubuntu and Debian. The document quality order from high to low is RHEL, Debian, Ubuntu. You do need to register an account to view most of the documents though.

Oracle Linux and Amazon Linux are derived from RHEL (or CentOS-stream, Fedora). If you run on Oracle Cloud or AWS, you may use these flavors. They behave similarly to RHEL and do not require a paid license to use. In comparison, the RHEL does require a license to use in mass production. There is a no-cost RHEL developer license that you can use in development environment and small production environment. There are a few community versions of RHEL re-pack when CentOS is acquired and discontinued by RedHat, such as RockyLinux and AlmaLinux. The offer binary compatibility with RHEL. But the default dnf repo and management tools are not all the same.

Ubuntu LTS, although the release is not as good as Debian, does have a large user base and a long term support (LTS). That makes it a much better choice than Ubuntu non-LTS release. Ubuntu LTS also got commercial support if you needs that. I found Ubuntu’s release not as stable as Debian. That’s why I always choose Debian over Ubuntu LTS. Only choose Ubuntu LTS only if you want to purchase support from Canonical.

I have not used OpenSUSE for real, so I won’t remark on them. Based on short experience of OpenSUSE Leap, the installer is very enterprisy. Side note: I think Open Build Service (e.g. OpenSUSE OBS) is a cool project, which works for all Linux projects and distros. But I haven’t tried it yet.

Edit: CentOS is acquired by RedHat and rebrand to CentOS stream. Added notes on Oracle Linux, Amazon Linux and some CentOS remakes.

If you need advice on choosing a Linux distro, you can leave a comment or email me. Do tell me what you want to do with Linux so the advice could be specific to your use case.

Here are software that I use often in Linux.

General

Programming

System

Office

Old

Software that I have used before, but no longer use it now.