How to check if ISO is bootable in Linux – From Command Line

So you have downloaded an iso which could be a linux installation or live iso or a windows iso or something other operating system. Now if you are planning to burn it to an actual disk like a cd or dvd, it would be a nice idea to first check if the iso if properly bootable or not.

This will confirm that the iso is bootable and is going to work the same way when used from an external media like dvd.

1. isoinfo command

To check if the iso is bootable, check the headers using the isoinfo command. In this example we shall use the ubuntu live server iso which is bootable and used to installed ubuntu server.

$ isoinfo -d -i ubuntu-23.04-live-server-amd64.iso 
CD-ROM is in ISO 9660 format
System id: 
Volume id: Ubuntu-Server 23.04 amd64
Volume set id: 
Publisher id: 
Data preparer id: XORRISO-1.5.2 2019.10.26.180001, LIBISOBURN-1.5.2, LIBISOFS-1.5.2, LIBBURN-1.5.2
Application id: 
Copyright File id: 
Abstract File id: 
Bibliographic File id: 
Volume set size is: 1
Volume set sequence number is: 1
Logical block size is: 2048
Volume size is: 1289680
El Torito VD version 1 found, boot catalog is in sector 790
Joliet with UCS level 3 found
Rock Ridge signatures version 1 found
Eltorito validation header:
    Hid 1
    Arch 0 (x86)
    ID ''
    Key 55 AA
    Eltorito defaultboot header:
        Bootid 88 (bootable)
        Boot media 0 (No Emulation Boot)
        Load segment 0
        Sys type 0
        Nsect 4
        Bootoff 317 791
enlightened@enlightened:/media/enlightened/a935afc9-17fd-4de1-8012-137e82662ff0/downloads$

Check the section titled: Eltorito validation header. It indicates that the iso is bootable. To learn more about El Torito check the wikipedia section here:

Lets run the same common on Windows 10 Installer iso that can be downloaded from microsoft.com for free.

$ isoinfo -d -i Win10_22H2_English_x64.iso 
CD-ROM is in ISO 9660 format
System id: 
Volume id: CCCOMA_X64FRE_EN-US_DV9
Volume set id: CCCOMA_X64FRE_EN-US_DV9
Publisher id: MICROSOFT CORPORATION
Data preparer id: MICROSOFT CORPORATION, ONE MICROSOFT WAY, REDMOND WA 98052, (425) 882-8080
Application id: CDIMAGE 2.56 (01/01/2005 TM)
Copyright File id: 
Abstract File id: 
Bibliographic File id: 
Volume set size is: 1
Volume set sequence number is: 1
Logical block size is: 2048
Volume size is: 2985931
El Torito VD version 1 found, boot catalog is in sector 22
NO Joliet present
NO Rock Ridge present
Eltorito validation header:
    Hid 1
    Arch 0 (x86)
    ID 'Microsoft Corporation'
    Key 55 AA
    Eltorito defaultboot header:
        Bootid 88 (bootable)
        Boot media 0 (No Emulation Boot)
        Load segment 0
        Sys type 0
        Nsect 8
        Bootoff 202 514
$

In the windows 10 iso also, we can see the Eltorito header, confirming that its a bootable disk image.

2. "file" command

The file command will indicate if the file is bootable. Here is the output for the same ubuntu server live iso file.

$ file ubuntu-23.04-live-server-amd64.iso 
ubuntu-23.04-live-server-amd64.iso: ISO 9660 CD-ROM filesystem data (DOS/MBR boot sector) 'Ubuntu-Server 23.04 amd64' (bootable)
$

Note the "(bootable)" string towards the end of the line.

Doing the same for the windows 10 installer iso

$ file Win10_22H2_English_x64.iso 
Win10_22H2_English_x64.iso: ISO 9660 CD-ROM filesystem data 'CCCOMA_X64FRE_EN-US_DV9' (bootable)
$

We can see that it reports the windows 10 iso as bootable as well.

3. Boot with Qemu

This is a more advanced way of checking whether the iso is bootable or not. It will actually boot it up in a virtualised environment using Qemu emulator.

The command is actually quite simple

$ qemu-system-x86_64 --enable-kvm -cpu host -boot d -m 2048 -cdrom ubuntu-23.04-live-server-amd64.iso

This will popup a Qemu virtual machine gui window and try booting the device. Note that this will indicate whether the iso is bootable or not, but it is not guaranteed to successfully boot the iso in anyway depending on what os is in the iso.