Explaining behaviour of sudo bash "$0" "$@"; Post: 303025441

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Top Forums Shell Programming and Scripting Explaining behaviour of sudo bash "$0" "$@"; Post 303025441 by Corona688 on Friday 2nd of November 2018 11:50:27 AM

11-02-2018

Registered User

For starters, you almost never need to use $?, a normal if-statement will do. Written this way, you can kind of see the logic. "If not sudo, then ..."

Not sure if it's really a simplification but I'd add >&2, the traditional place for error messages. That way if someone uses this in a stream they can direct data output and error output separately.

You should have an exit after exec, in case the exec fails for whatever reason (i.e. path problems or something).

Then I'd label the section which is always intended to run as root.

Code:

#!/bin/bash

# If we can't run sudo without a password, complain and exit
if ! sudo -n true 2> /dev/null
then
       echo "please run as root" >&2
       echo "haha you have not power here" >&2
       echo "You need to enter password" >&2
       
       # Not sure if you want this or not?  Exits after printing error/warning
       exit 1
fi

# If EUID isn't zero, replace and re-run this script as root using sudo.
if [ "$EUID" -ne 0 ]
then
        exec sudo bash "$0" "$@"
        echo "exec failed" >&2
        exit 1
fi

#########################################
####### The below section always runs as root #########
#########################################

declare commandOutput=$(apt-add-repository multiverse);
if echo "$commandOutput" | grep -q "distribution component is already enabled"; then 
  echo "multiverse repository is already enabled" >&2
fi

The "replace and re-run" bit comes down to how exec really works: It causes the running program to replace itself with what you ask. Whether it succeeds or fails, after an

The >&2's make more likely that these messages get printed to the terminal, where these messages usually belong.

More could probably be done with apt-get, like checking its return value rather than just assuming it operates correctly.

Last edited by Corona688; 11-02-2018 at 12:56 PM..

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LEARN ABOUT XFREE86

pivot_root

PIVOT_ROOT(8)						       System Administration						     PIVOT_ROOT(8)

NAME

       pivot_root - change the root filesystem

SYNOPSIS

       pivot_root new_root put_old

DESCRIPTION

       pivot_root  moves  the root file system of the current process to the directory put_old and makes new_root the new root file system.  Since
       pivot_root(8) simply calls pivot_root(2), we refer to the man page of the latter for further details.

       Note that, depending on the implementation of pivot_root, root and cwd of the caller may or may not change. The following is a sequence for
       invoking pivot_root that works in either case, assuming that pivot_root and chroot are in the current PATH:

       cd new_root
       pivot_root . put_old
       exec chroot . command

       Note that chroot must be available under the old root and under the new root, because pivot_root may or may not have implicitly changed the
       root directory of the shell.

       Note that exec chroot changes the running executable, which is necessary if the old root directory should be  unmounted	afterwards.   Also
       note  that  standard  input, output, and error may still point to a device on the old root file system, keeping it busy. They can easily be
       changed when invoking chroot (see below; note the absence of leading slashes to make it work whether pivot_root	has  changed  the  shell's
       root or not).

OPTIONS

       -V, --version
	      Display version information and exit.

       -h, --help
	      Display help text and exit.

EXAMPLES

       Change the root file system to /dev/hda1 from an interactive shell:

       mount /dev/hda1 /new-root
       cd /new-root
       pivot_root . old-root
       exec chroot . sh <dev/console >dev/console 2>&1
       umount /old-root

       Mount the new root file system over NFS from 10.0.0.1:/my_root and run init:

       ifconfig lo 127.0.0.1 up   # for portmap
       # configure Ethernet or such
       portmap	 # for lockd (implicitly started by mount)
       mount -o ro 10.0.0.1:/my_root /mnt
       killall portmap	 # portmap keeps old root busy
       cd /mnt
       pivot_root . old_root
       exec chroot . sh -c 'umount /old_root; exec /sbin/init' 
	 <dev/console >dev/console 2>&1

SEE ALSO

       chroot(1), pivot_root(2), mount(8), switch_root(8), umount(8)

AVAILABILITY

       The pivot_root command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux							    August 2011 						     PIVOT_ROOT(8)