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49 lines
1.9 KiB
49 lines
1.9 KiB
5 years ago
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Dracut supports running against a sysroot directory that is different
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from the actual root (/) directory of the running system. It is most
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useful for creating/bootstrapping a new system that may or may not be
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using the same CPU architecture as the host system, i.e. building a
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whole Linux system with a cross-compiler framework like Yocto.
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The user-visible frontend change is the introduction of a new option
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called "-r" or "--sysroot". It expects a directory that contains the
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complete Linux system that has all the files (kernel drivers, firmware,
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executables, libraries and others) necessary to construct the initramfs.
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E.g: dracut --sysroot /path/to/sysroot initramfs.img kernelversion
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To support this, a new global variable was introduced inside dracut.
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This variable is called "dracutsysrootdir" and all the files installed
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into the initramfs image is searched relative to the sysroot directory.
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This variable can also be set externally to dracut without using option
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-r/--sysroot.
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There are other details that are necessary to tweak to be able to
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run on cross-compiled (a.k.a. foreign) binaries.
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dracut uses these crucial utilities during its operation:
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ldd
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===
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It lists dynamic library dependencies for executables or libraries
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ldconfig
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========
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It creates /etc/ld.so.cache, i.e. the cached information about libraries
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known to the system.
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These utilities the way they exist on the host system only work on
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the host system.
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To support cross-compiled binaries, a different ldd variant is needed that
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works on those binaries. One such ldd script is found at
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https://gist.github.com/jerome-pouiller/c403786c1394f53f44a3b61214489e6f
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ldconfig in GLIBC as is does support a sysroot with its -r option.
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Extra environment variables needed to run dracut on the sysroot are
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documented in the dracut(8) man page.
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For the Plymouth boot splash to be added to the initramfs image,
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this gitlab PR is needed for Plymouth:
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https://gitlab.freedesktop.org/plymouth/plymouth/merge_requests/72
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