Why /etc/profile needs to be sourced after chroot?

[avidseeker]

Not directly related to Gentoo, but the way I understand it is that /etc/profile is sourced on interactive shell session (bash) automatically.
This is what I'm used to (at least coming from Arch Linux). I am wondering why is the behavior different?

[Zucca]

By sourcing /etc/profile you'll set all the necessary environment variables (among other things) inside the chroot.
If you know shell scripting, then see what's inside the /etc/profile and learn. ;)

[avidseeker]

Yes I know about the environment variables it sets. My questions is that since the first command in the chroot is bash, shouldn't bash automatically source /etc/profile?

More concretely, I have two partitions one with an Arch system and one with a Gentoo system. Why is chrooting to Arch automatically sources /etc/profile, while chrooting to Gentoo doesn't?

[Banana]

Then you have to check if there is a difference in the startup files: https://www.gnu.org/software/bash/manua ... Files.html

[avidseeker]

This is the path after su -:

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root ~ # echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin:/usr/lib/llvm/17/bin

I'm trying to understand what file is setting the path here.

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root ~ # echo ~/.bash*
/root/.bash_history

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root ~ # cat /etc/profile

if [ -n "${BASH_VERSION-}" ] ; then
        # Newer bash ebuilds include /etc/bash/bashrc which will setup PS1
        # including color.  We leave out color here because not all
        # terminals support it.
        if [ -f /etc/bash/bashrc ] ; then
                # Bash login shells run only /etc/profile
                # Bash non-login shells run only /etc/bash/bashrc
                # Since we want to run /etc/bash/bashrc regardless, we source it
                # from here.  It is unfortunate that there is no way to do
                # this *after* the user's .bash_profile runs (without putting
                # it in the user's dot-files), but it shouldn't make any
                # difference.
                . /etc/bash/bashrc
        else
                PS1='\u@\h \w \$ '
        fi
fi

But checking /etc/bash/bashrc, I don't see any relevant function updating PATH.

In Arch, there is append_path function in /etc/profile.

[grknight]

A lot of the "Gentoo magic" happens in /etc/profile.env which is created by our env-update tool. This is read in much earlier in /etc/profile:

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# Load environment settings from profile.env, which is created by
# env-update from the files in /etc/env.d
if [ -e /etc/profile.env ] ; then
	. /etc/profile.env
fi

env-update reads in lots of settings from /etc/env.d and compiles them into /etc/profile.env or /etc/ld.so.conf as needed.

[avidseeker]

Oh, I overlooked this. This clears some things up.

Now back to my original question. Doesn't bash source /etc/profile by default? which sources /etc/profile.env?

Then why is /etc/profile needed to be sourced manually?

The gnu manual says that:

When Bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile.

The only way I can think of is that bash doesn't regard chrooting as login?

[Zucca]

The gnu manual says that:

When Bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile.

The only way I can think of is that bash doesn't regard chrooting as login?

Interesting. I've never thought of this. I wonder if

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chroot /mnt/gentoo /bin/bash -l

... forces sourcing of /etc/profile.

[Goverp]

Following the above, I've tweaked an old script I use to build my chroot. It's benefit is I can write things like the following, and just edit the list of mounts:

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# Mounts below must be absolute, starting with a / . They can have source=mountpoint
mounts="/proc /sys /dev /run /usr/local/bin /boot /usr/src /lib/modules /usr/local/overlay /var/cache/binpkgs /var/cache/distfiles /var/db/repos"
chroot=~packager/chroot
path="${0%/*}"   # The build-chroot script is in the same directory as this script
"$path"/build-chroot "$chroot" $mounts

build-chroot:

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#! /bin/sh

# Recursively bind-mount a series of directories within a target directory
# then chroot into that target directory,
# and after exiting the chroot, umount all the bind mounts
# so as to leave the mount enviroment back in its original state

# Syntax : build-chroot <target directory> <directories to be recusively bind-mounted>
# N. B. the directories to be mounted MUST be specified as absolute paths

# goverp 7 Mar 2020
# updated 25 Feb 2024 to start bash with "_l" to cause it to execute /etc/profile - thanks Zucca

chroot="$1"
shift
mounts="$*"

# $umounts will be the list of directories mounted, but in reverse order
umounts=""

# Recursively bind-mount the directories, and make them rslaves to keep changes within the chroot
for dir in $mounts
do
        target="${dir#*=}"
        if      [ "$target" != "$dir" ]
        then    dir="${dir%%=$target}"
        fi

        target="${chroot}/${target}"
        mount --rbind "$dir" "$target"
        mount --make-rslave "$target"
        umounts="$target $umounts"
done

# Enter the chroot environment
WHENCE="$chroot" chroot "$chroot" /bin/bash -l

# Unmount the mounted directories in reverse order, handling submounts
for target in $umounts
do
        umount -R "$target"
done

I also have a ~/.bash_profile in the chroot that

1. does a cd ~ so I end up in my chroot's root home directory instead of "/";
2. alters the prompt so I know I'm in the chroot; and
3. lets me set environment variable CHROOT_COMMAND if I want to execute something:

~/.bash_profile

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#!/bin/sh
cd ~

PS1="CHROOT ${WHENCE} \u \w #"

[ -x "$CHROOT_COMMAND" ] && $CHROOT_COMMAND

[Hu]

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# and after exiting the chroot, umount all the bind mounts

Depending on your use case, you might be able to simplify this by using a mount namespace for the chroot, so that the mounts are automatically cleaned out when the last process from the chroot exits. This also avoids them showing up in /proc/mounts for non-chroot processes, which may make the output cleaner. To use a mount namespace, run the entire chroot-building script under /usr/bin/unshare -m. See man unshare for details.

You can also rig the build-chroot script to re-invoke itself under unshare if you want to keep the caller simpler.

[avidseeker]

Following the above, I've tweaked an old script I use to build my chroot. It's benefit is I can write things like the following, and just edit the list of mounts:

I'm still using the convenient arch-chroot wrapper script from arch-install-scripts. The script also takes care of umounting.
You might find it interesting and useful for adapting it to your script.

[avidseeker]

Interesting. I've never thought of this. I wonder if

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chroot /mnt/gentoo /bin/bash -l

... forces sourcing of /etc/profile.

Here are my findings:

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[root@Host ~]# chroot /mnt /bin/bash
Host / # which ls
which: no ls in (/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/default/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl)
Host / # echo $PATH | tr : "\n"
/usr/local/sbin
/usr/local/bin
/usr/bin
/usr/lib/jvm/default/bin
/usr/bin/site_perl
/usr/bin/vendor_perl
/usr/bin/core_perl

However,

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[root@Host ~]# chroot /mnt /bin/bash -l
Host / # which ls
/bin/ls
Host / # echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin:/usr/lib/llvm/17/bin

If /bin/bash without --login doesn't load /etc/profile, then what is setting the PATH?