OS Customization

The instructions on this page only apply to Linux installations.

Partitioning

The OS will be installed on the first disk. NVME drives will be preferred, if a server has multiple disk types.

Default Linux Disk Partitions

By default, regular Linux installations will have the following partitioning details:

Partitions:

• /boot, 4096MB

• /, using the remaining space on the disk

• swap is enabled and has a size of 8192MB

Custom Partitioning

During new server requests, it is possible to provide your own partitioning scheme.

In the partitions field of the OS object, you can customize your Linux partitions by specifying a list of them. Each partition object should have the following fields:

Field	Type	Description	Example Value
target	string	The mount point for the partition	/boot
filesystem	string	The filesystem to use for the target. Currently supported types: ext2, ext3, ext4, xfs	ext4
size	int	The size of the partition in MB, or -1 for the remaining disk space	4096

Example

{
    "name": "MyFlexServer",
    "location": "EU: Rotterdam",
    "instanceType": "bm7.std.8",
    "os": {
        "slug": "ubuntu-2404-lts",
        "partitions": [
            {
                "target": "/boot",
                "filesystem": "ext4",
                "size": 4096
            },
            {
                "target": "/",
                "filesystem": "ext4",
                "size": -1
            },
            {
                "target": "/custom",
                "filesystem": "ext4",
                "size": 10240
            },
            {
                "target": "swap",
                "size": 8192
            }
        ]
    },
    "sshKey": [
        "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIWrzxdeW3hhkejzSfFBFzPzcEBJBGtggOUJpLBCakbqmV/NztCaUoh631Xnk46MFn2snF89tSZZzlp9ySpqW7c= ecdsa-key-example"
    ],
    "postInstallScript": "#!/bin/bash\necho \"Hello flex world\" > /tmp/test.txt",
    "tags": [
        "My-tag1",
        "env:dev"
    ]
}

• The / and /boot partitions are required and must be defined.

• The size field is in MB.

• The size field can be -1 to use the remaining disk space.

• To disable the swap file, omit the swap partition from the list of partitions.

• Accepted filesystems: ext2, ext3, ext4, xfs.

• Partitioning does not apply to Talos installations, because Talos does not support customizing partitions.

The Linux bootloader

Default bootloader options

During the OS installation process, we apply a specific customization to enable legacy network interface naming. This ensures that network interfaces follow the traditional ethX naming convention for OS install compatibility reasons.

The following kernel parameters are set:

• net.ifnames=0: Disables predictable network interface names.

• biosdevname=0: Disables naming based on BIOS device names.

No additional options are configured by default.

Customizing the bootloader

Incorrect kernel arguments can prevent the server from booting. Please ensure that you provide valid kernel arguments.

You can provide additional kernel arguments to the bootloader by specifying them in the kernelParams field of the OS object when you request a new server. These values will be added to the GRUB configuration file and applied as follows:

• Add the kernel parameters to the GRUB_CMDLINE_LINUX variable in /etc/default/grub

• Update the GRUB configuration with update-grub (Debian based systems) or grub2-mkconfig -o /boot/grub/grub.cfg (RH / Centos based systems)

  • This generates the grub.cfg file and generates the /boot/grub/grubenv file

Example

In the kernelParams field of the OS object, you can provide a list of custom kernel or GRUB parameters. For example:

{
    "name": "MyFlexServer",
    "location": "EU: Rotterdam",
    "instanceType": "bm7.std.8",
    "os": {
        "slug": "ubuntu-2404-lts",
        "kernelParams": [
            {
                "key": "mitigations",
                "value": "auto,nosmt"
            },
            {
                "key": "nopti",
                "value": ""
            }
        ],
    },
    "sshKey": [
        "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIWrzxdeW3hhkejzSfFBFzPzcEBJBGtggOUJpLBCakbqmV/NztCaUoh631Xnk46MFn2snF89tSZZzlp9ySpqW7c= ecdsa-key-example"
    ],
    "postInstallScript": "#!/bin/bash\necho \"Hello flex world\" > /tmp/test.txt",
    "tags": [
        "My-tag1",
        "env:dev"
    ]
}

This example disables hyperthreading (on the OS level) and disables Page Table Isolation (PTI) in the kernel. The options added to the GRUB configuration are: mitigations=auto,nosmt nopti.

Talos Linux requires special kernel arguments to boot. Please refer to the Talos installation documentation for more details.