Trait std::os::unix::process::CommandExt

1.0.0 · source ·
pub trait CommandExt: Sealed {
    // Required methods
    fn uid(&mut self, id: u32) -> &mut Command;
    fn gid(&mut self, id: u32) -> &mut Command;
    fn groups(&mut self, groups: &[u32]) -> &mut Command;
    unsafe fn pre_exec<F>(&mut self, f: F) -> &mut Command
       where F: FnMut() -> Result<()> + Send + Sync + 'static;
    fn exec(&mut self) -> Error;
    fn arg0<S>(&mut self, arg: S) -> &mut Command
       where S: AsRef<OsStr>;
    fn process_group(&mut self, pgroup: i32) -> &mut Command;

    // Provided method
    fn before_exec<F>(&mut self, f: F) -> &mut Command
       where F: FnMut() -> Result<()> + Send + Sync + 'static { ... }
Available on Unix only.
Expand description

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

This trait is sealed: it cannot be implemented outside the standard library. This is so that future additional methods are not breaking changes.

Required Methods§

1.0.0 · source

fn uid(&mut self, id: u32) -> &mut Command

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 will also trigger a call to setgroups(0, NULL) in the child process if no groups have been specified. This removes supplementary groups that might have given the child unwanted permissions.

1.0.0 · source

fn gid(&mut self, id: u32) -> &mut Command

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


fn groups(&mut self, groups: &[u32]) -> &mut Command

🔬This is a nightly-only experimental API. (setgroups #90747)

Sets the supplementary group IDs for the calling process. Translates to a setgroups call in the child process.

1.34.0 · source

unsafe fn pre_exec<F>(&mut self, f: F) -> &mut Command
where F: FnMut() -> Result<()> + Send + Sync + 'static,

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.

§Notes and Safety

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, accessing environment variables through std::env or acquiring a mutex are not guaranteed to work (due to other threads perhaps still running when the fork was run).

For further details refer to the POSIX fork() specification and the equivalent documentation for any targeted platform, especially the requirements around async-signal-safety.

This also means that all resources such as file descriptors and memory-mapped regions got duplicated. It is your responsibility to make sure that the closure does not violate library invariants by making invalid use of these duplicates.

Panicking in the closure is safe only if all the format arguments for the panic message can be safely formatted; this is because although Command calls std::panic::always_abort before calling the pre_exec hook, panic will still try to format the panic message.

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

1.9.0 · source

fn exec(&mut self) -> Error

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.

1.45.0 · source

fn arg0<S>(&mut self, arg: S) -> &mut Command
where S: AsRef<OsStr>,

Set executable argument

Set the first process argument, argv[0], to something other than the default executable path.

1.64.0 · source

fn process_group(&mut self, pgroup: i32) -> &mut Command

Sets the process group ID (PGID) of the child process. Equivalent to a setpgid call in the child process, but may be more efficient.

Process groups determine which processes receive signals.


Pressing Ctrl-C in a terminal will send SIGINT to all processes in the current foreground process group. By spawning the sleep subprocess in a new process group, it will not receive SIGINT from the terminal.

The parent process could install a signal handler and manage the subprocess on its own terms.

A process group ID of 0 will use the process ID as the PGID.

use std::process::Command;
use std::os::unix::process::CommandExt;


Provided Methods§

1.15.0 · source

fn before_exec<F>(&mut self, f: F) -> &mut Command
where F: FnMut() -> Result<()> + Send + Sync + 'static,

👎Deprecated since 1.37.0: should be unsafe, use pre_exec instead

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

This method is stable and usable, but it should be unsafe. To fix that, it got deprecated in favor of the unsafe pre_exec.

Object Safety§

This trait is not object safe.


1.0.0 · source§

impl CommandExt for Command