diff options
Diffstat (limited to 'man2/pivot_root.2')
| -rw-r--r-- | man2/pivot_root.2 | 60 |
1 files changed, 29 insertions, 31 deletions
diff --git a/man2/pivot_root.2 b/man2/pivot_root.2 index d56ad996c..a4077ef73 100644 --- a/man2/pivot_root.2 +++ b/man2/pivot_root.2 @@ -4,7 +4,7 @@ .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" -.TH pivot_root 2 2023-02-05 "Linux man-pages 6.03" +.TH pivot_root 2 2023-05-03 "Linux man-pages 6.05.01" .SH NAME pivot_root \- change the root mount .SH LIBRARY @@ -151,12 +151,10 @@ is a mount point and has the propagation type The calling process does not have the .B CAP_SYS_ADMIN capability. -.SH VERSIONS -.BR pivot_root () -was introduced in Linux 2.3.41. .SH STANDARDS -.BR pivot_root () -is Linux-specific and hence is not portable. +Linux. +.SH HISTORY +Linux 2.3.41. .SH NOTES A command-line interface for this system call is provided by .BR pivot_root (8). @@ -302,7 +300,7 @@ hello world .\" SRC BEGIN (pivot_root.c) .EX /* pivot_root_demo.c */ - +\& #define _GNU_SOURCE #include <err.h> #include <limits.h> @@ -316,15 +314,15 @@ hello world #include <sys/syscall.h> #include <sys/wait.h> #include <unistd.h> - +\& static int pivot_root(const char *new_root, const char *put_old) { return syscall(SYS_pivot_root, new_root, put_old); } - +\& #define STACK_SIZE (1024 * 1024) - +\& static int /* Startup function for cloned child */ child(void *arg) { @@ -332,70 +330,70 @@ child(void *arg) char **args = arg; char *new_root = args[0]; const char *put_old = "/oldrootfs"; - +\& /* Ensure that \[aq]new_root\[aq] and its parent mount don\[aq]t have shared propagation (which would cause pivot_root() to return an error), and prevent propagation of mount events to the initial mount namespace. */ - +\& if (mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL) == \-1) err(EXIT_FAILURE, "mount\-MS_PRIVATE"); - +\& /* Ensure that \[aq]new_root\[aq] is a mount point. */ - +\& if (mount(new_root, new_root, NULL, MS_BIND, NULL) == \-1) err(EXIT_FAILURE, "mount\-MS_BIND"); - +\& /* Create directory to which old root will be pivoted. */ - +\& snprintf(path, sizeof(path), "%s/%s", new_root, put_old); if (mkdir(path, 0777) == \-1) err(EXIT_FAILURE, "mkdir"); - +\& /* And pivot the root filesystem. */ - +\& if (pivot_root(new_root, path) == \-1) err(EXIT_FAILURE, "pivot_root"); - +\& /* Switch the current working directory to "/". */ - +\& if (chdir("/") == \-1) err(EXIT_FAILURE, "chdir"); - +\& /* Unmount old root and remove mount point. */ - +\& if (umount2(put_old, MNT_DETACH) == \-1) perror("umount2"); if (rmdir(put_old) == \-1) perror("rmdir"); - +\& /* Execute the command specified in argv[1]... */ - +\& execv(args[1], &args[1]); err(EXIT_FAILURE, "execv"); } - +\& int main(int argc, char *argv[]) { char *stack; - +\& /* Create a child process in a new mount namespace. */ - +\& 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"); - +\& if (clone(child, stack + STACK_SIZE, CLONE_NEWNS | SIGCHLD, &argv[1]) == \-1) err(EXIT_FAILURE, "clone"); - +\& /* Parent falls through to here; wait for child. */ - +\& if (wait(NULL) == \-1) err(EXIT_FAILURE, "wait"); - +\& exit(EXIT_SUCCESS); } .EE |