`mkdir` and `mkdirat` might set errno to EOVERFLOW when UID or GID mapping has not been configured. See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=036d523641c66bef713042894a17f4335f199e49 This is a small program in the commit message that shows this behavior: static int childFunc(void *_) { if (mount("tmpfs", "/tmp", "tmpfs", 0, NULL)) { err(EXIT_FAILURE, "mount"); } if (mkdir("/tmp/test", 0755) == -1) { err(EXIT_FAILURE, "mkdir"); } return 0; } int main(int argc, char *argv[]) { char *stack; /* Start of stack buffer */ char *stackTop; /* End of stack buffer */ pid_t pid; stack = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0); if (stack == MAP_FAILED) err(EXIT_FAILURE, "mmap"); stackTop = stack + STACK_SIZE; pid = clone(childFunc, stackTop, CLONE_NEWUSER | CLONE_NEWNS | SIGCHLD, NULL); if (munmap(stack, STACK_SIZE) == -1) err(EXIT_FAILURE, "munmap"); if (pid == -1) err(EXIT_FAILURE, "clone"); if (waitpid(pid, NULL, 0) == -1) err(EXIT_FAILURE, "waitpid"); exit(EXIT_SUCCESS); } Signed-off-by: Chen Linxuan <chenlinxuan@xxxxxxxxxxxxx> --- man/man2/mkdir.2 | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/man/man2/mkdir.2 b/man/man2/mkdir.2 index d84dbc27e..2af618d68 100644 --- a/man/man2/mkdir.2 +++ b/man/man2/mkdir.2 @@ -203,6 +203,10 @@ does not support the creation of directories. .B EROFS .I pathname refers to a file on a read-only filesystem. +.B EOVERFLOW +UID or GID mappings (see +.BR user_namespaces (7)) +has not been configured. .SH VERSIONS Under Linux, apart from the permission bits, the .B S_ISVTX -- 2.43.0
