fakeroot

Fakeroot is a user-space tool that simulates root privileges for the purposes of file ownership and permission changes during packaging and archiving. It allows a non-privileged user to create files and directories that appear to be owned by user ID 0, and to assign privileged metadata, without granting actual root access.

Operation and mechanism: Fakeroot works by using the LD_PRELOAD mechanism to load a small shared library that intercepts a broad set of system calls related to file metadata and ownership. The library overrides calls such as chown, chmod, mkdir, mknod, link, unlink, and various stat/fstat operations. It maintains an in-memory model of what the ownership and permissions would be if the process were running as root and applies these fake values to the observed metadata in created files and archives. The real kernel and filesystem are not modified; only the apparent metadata presented to the user space process and any produced artifacts reflect the simulated root privileges.

Typical usage: It is commonly employed when building packages (notably in Debian-based packaging workflows) or creating tar archives where final files should show root ownership. A build or packaging process is run under fakeroot, and the resulting package contents appear to be owned by root when installed, even though the build was performed by a non-privileged user. It is often used in combination with chroots, containers, or packaging tools like dpkg-buildpackage.

Limitations: Fakeroot does not provide actual superuser capabilities and cannot bypass all privilege checks. Some operations or kernel features may not be fully emulated, and certain filesystem-specific behaviors or extended attributes may not be replicable in all environments. It is intended for packaging and testing workflows, not for secure privilege elevation.