The sysctl utility allows a Linux admin to query and modify kernel parameters in runtime. For example, to change the swappiness of a linux system to 0 we can:

1. echo 0 > /proc/sys/vm/swappiness

Or we can use sysctl

2. sysctl -w vm.swappiness=0

To make the value persistent, Archwiki suggests to writevm.swappiness=0 to /etc/sysctl.d/99-swappiness.conf file.

For persistent silent boot, Archwiki suggests to write kernel.printk = 3 3 3 3 to /etc/sysctl.d/20-quiet-printk.conf

Similarly I have a 99-sysrq.conf on my system which works without the number as well.

Archwiki has a sysctl page which mentions the importance of the number:

Note: From version 207 and 21x, systemd only applies settings from /etc/sysctl.d/.conf and /usr/lib/sysctl.d/.conf. If you had customized /etc/sysctl.conf, you need to rename it as /etc/sysctl.d/99-sysctl.conf. If you had e.g. /etc/sysctl.d/foo, you need to rename it to /etc/sysctl.d/foo.conf.

What does the number in 99-swappiness.conf and 20-quiet-printk.conf denote here?

The sysctl utility allows a Linux admin to query and modify kernel parameters in runtime. For example, to change the swappiness of a Linux system to 0, we can:

1. echo 0 > /proc/sys/vm/swappiness

Or we can use sysctl:

2. sysctl -w vm.swappiness=0

To make the value persistent, Archwiki suggests to write  vm.swappiness=0 to /etc/sysctl.d/99-swappiness.conf file.

For persistent silent boot, Archwiki suggests to write kernel.printk = 3 3 3 3 to /etc/sysctl.d/20-quiet-printk.conf

Similarly I have a 99-sysrq.conf on my system which works without the number as well.

Archwiki has a sysctl page which mentions the importance of the number:

Note: From version 207 and 21x, systemd only applies settings from /etc/sysctl.d/*.conf and /usr/lib/sysctl.d/*.conf.  If you had customized /etc/sysctl.conf, you need to rename it as /etc/sysctl.d/99-sysctl.conf.  If you had e.g. /etc/sysctl.d/foo, you need to rename it to /etc/sysctl.d/foo.conf.

What does the number in 99-swappiness.conf and 20-quiet-printk.conf denote here?