fakeroot-tcp

fakeroot-tcp [OPTIONS] COMMAND [ARGUMENTS...]

--help, -h
    Displays a help message and exits.

--version, -v
    Displays version information and exits.

--debug
    Prints debugging information to stderr, which can be useful for troubleshooting.

--
    Used to separate fakeroot-tcp options from the options of the COMMAND to be executed. Any arguments after this are treated as part of the COMMAND.

The fakeroot-tcp command is a variant of the fakeroot utility, designed to simulate root privileges (UID 0, GID 0) for a given command without actually granting them. This is primarily achieved by intercepting library calls that perform file system operations (like stat, chmod, chown, mkdir, mknod, etc.) and modifying their reported results.

The key distinction of fakeroot-tcp from the standard fakeroot is its communication mechanism. Instead of using shared memory or FIFOs (which are common IPC methods for fakeroot), fakeroot-tcp utilizes TCP sockets to communicate between the main fakeroot process (the daemon) and the processes running under the fake root environment. This makes it particularly useful in restricted environments, such as chroot jails or containers, where traditional IPC mechanisms might be disabled, unavailable, or have complex permission requirements, thus providing a more robust and flexible solution for creating build environments or testing scripts that require root access.

Not a Security Mechanism: fakeroot-tcp does not provide actual root privileges and should not be used as a security tool. It can be easily bypassed by malicious code or applications that don't rely on standard library calls for file system operations.

Limited Scope: It only fakes file system ownership and permissions. Operations requiring actual kernel privileges, such as loading kernel modules, mounting file systems, or specific device access, will fail.

Performance Overhead: Intercepting system calls and communicating via TCP sockets introduces a slight performance overhead compared to native execution.

Environment Dependencies: Relies on the LD_PRELOAD mechanism, which might not work with statically linked binaries or in environments configured to prevent library preloading for security reasons.

fakeroot-tcp operates by using the LD_PRELOAD mechanism to inject a library into the executed command's environment. This library intercepts relevant system calls (e.g., stat, chmod, chown). Instead of passing these calls directly to the kernel, the library communicates with a separate fakeroot daemon process (typically the parent fakeroot-tcp process itself). This daemon maintains an internal database mapping real UIDs/GIDs and permissions to fake root (0/0) or other simulated values. The communication between the intercepted library and the daemon is performed over a TCP socket, allowing fakeroot-tcp to work even when traditional shared memory or FIFO pipes are not available or restricted.

The original fakeroot utility was developed by Lennart Poettering, Joost Kooijman, and others, primarily to allow unprivileged users to build software packages (like Debian packages) that require root privileges during the build process to set correct file ownership and permissions. The fakeroot-tcp variant was later introduced to address specific limitations of the default IPC mechanisms (FIFOs, shared memory) in certain environments, particularly within chroot jails or containers, where TCP communication offered a more reliable and flexible alternative.

fakeroot(1), chroot(1), unshare(1), sudo(8)