what is the difference between dracut -a and dracut -m?

[Masber]

Dear dracut community,

I am trying to create an initramfs file using dracut, I need to add a few modules to it but could not figure out which option is best (-a or -m) I tried both and I am getting different results. My configusion comes because I have the impression -a option tries to install modules not specified in the modules list.

dracut -f -v -M -a "bash systemd warpclock systemd-initrd systemd-networkd modsign rescue watchdog i18n convertfs network-legacy network-manager cray-network network cray-netif ifcfg url-lib drm plymouth lvmmerge crypt dm kernel-modules kernel-modules-extra kernel-network-modules lvm mdraid multipath qemu qemu-net crypt-gpg crypt-loop craychrony cray-spire debug fcoe fcoe-uefi iscsi lunmask nfs nvmf resume rootfs-block ssh-client terminfo udev-rules virtfs biosdevname craylnet crayurl dracut-systemd haveged pollcdrom selinux syslog usrmount base fs-lib shutdown squash uefi-lib" initrd.img
dracut: Executing: /usr/bin/dracut -f -v -M -a "bash systemd warpclock systemd-initrd systemd-networkd modsign rescue watchdog i18n convertfs network-legacy network-manager cray-network network cray-netif ifcfg url-lib drm plymouth lvmmerge crypt dm kernel-modules kernel-modules-extra kernel-network-modules lvm mdraid multipath qemu qemu-net crypt-gpg crypt-loop craychrony cray-spire debug fcoe fcoe-uefi iscsi lunmask nfs nvmf resume rootfs-block ssh-client terminfo udev-rules virtfs biosdevname craylnet crayurl dracut-systemd haveged pollcdrom selinux syslog usrmount base fs-lib shutdown squash uefi-lib" initrd.img
dracut: dracut module 'network-wicked' will not be installed, because command 'wicked' could not be found!
dracut: 62bluetooth: Could not find any command of '/usr/lib/bluetooth/bluetoothd /usr/libexec/bluetooth/bluetoothd'!
dracut: dracut module 'btrfs' will not be installed, because command 'btrfs' could not be found!
dracut: dracut module 'dmraid' will not be installed, because command 'dmraid' could not be found!
dracut: dracut module 'mdraid' will not be installed, because command 'mdadm' could not be found!
dracut: dracut module 'tpm2-tss' will not be installed, because command 'tpm2' could not be found!
dracut: dracut module 'cifs' will not be installed, because command 'mount.cifs' could not be found!
dracut: dracut module 'iscsi' will not be installed, because command 'iscsi-iname' could not be found!
dracut: dracut module 'iscsi' will not be installed, because command 'iscsiadm' could not be found!
dracut: dracut module 'iscsi' will not be installed, because command 'iscsid' could not be found!
dracut: 95nfs: Could not find any command of 'rpcbind portmap'!
dracut: dracut module 'nvmf' will not be installed, because command 'nvme' could not be found!
dracut: dracut module 'biosdevname' will not be installed, because command 'biosdevname' could not be found!
dracut: dracut module 'memstrack' will not be installed, because command 'memstrack' could not be found!
dracut: memstrack is not available
dracut: If you need to use rd.memdebug>=4, please install memstrack and procps-ng
dracut: dracut module 'cray-network' cannot be found or installed.

Note: when I try with -m I get a shorter list of problems, all related to the modules listed in the command.

1. Why is -a trying to install modules (eg btrfs) that are not on the list?
2. what's the difference between -a and -m?

thank you very much

[aafeijoo-suse]

-m : only include these modules
-a : append these modules to the list of modules that would be added anyway

Usually you should build a hostonly initrd (-H), so dracut will include only the minimal list of modules to boot your system, and add (-a) the modules you always want to be there (if they are not added automatically with -H).