Trait std::os::unix::process::CommandExt1.0.0 [] [src]

pub trait CommandExt {
    fn uid(&mut self, id: u32) -> &mut Command;
fn gid(&mut self, id: u32) -> &mut Command;
fn before_exec<F>(&mut self, f: F) -> &mut Command
        F: FnMut() -> Result<()> + Send + Sync + 'static
fn exec(&mut self) -> Error; }
This is supported on Unix only.

Unix-specific extensions to the std::process::Command builder

Required Methods

This is supported on Unix only.

Sets the child process's user id. This translates to a setuid call in the child process. Failure in the setuid call will cause the spawn to fail.

This is supported on Unix only.

Similar to uid, but sets the group id of the child process. This has the same semantics as the uid field.

This is supported on Unix only.

Schedules a closure to be run just before the exec function is invoked.

The closure is allowed to return an I/O error whose OS error code will be communicated back to the parent and returned as an error from when the spawn was requested.

Multiple closures can be registered and they will be called in order of their registration. If a closure returns Err then no further closures will be called and the spawn operation will immediately return with a failure.


This closure will be run in the context of the child process after a fork. This primarily means that any modifications made to memory on behalf of this closure will not be visible to the parent process. This is often a very constrained environment where normal operations like malloc or acquiring a mutex are not guaranteed to work (due to other threads perhaps still running when the fork was run).

When this closure is run, aspects such as the stdio file descriptors and working directory have successfully been changed, so output to these locations may not appear where intended.

This is supported on Unix only.

Performs all the required setup by this Command, followed by calling the execvp syscall.

On success this function will not return, and otherwise it will return an error indicating why the exec (or another part of the setup of the Command) failed.

exec not returning has the same implications as calling process::exit – no destructors on the current stack or any other thread’s stack will be run. Therefore, it is recommended to only call exec at a point where it is fine to not run any destructors. Note, that the execvp syscall independently guarantees that all memory is freed and all file descriptors with the CLOEXEC option (set by default on all file descriptors opened by the standard library) are closed.

This function, unlike spawn, will not fork the process to create a new child. Like spawn, however, the default behavior for the stdio descriptors will be to inherited from the current process.


The process may be in a "broken state" if this function returns in error. For example the working directory, environment variables, signal handling settings, various user/group information, or aspects of stdio file descriptors may have changed. If a "transactional spawn" is required to gracefully handle errors it is recommended to use the cross-platform spawn instead.