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[[!meta copyright="Copyright © 2024 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
[[!tag stable_URL]]
The remap translator lets you remap directories. This translator is to
be used as a chroot, within which paths point to the same files as the
original root, except a given set of paths, which are remapped to given
paths.
This translator completes the [[server
overriding|community/gsoc/project_ideas/server_overriding]] google
summer of code project.
It is often desirable to execute a command in a transitory environment
with remapped files. The `remap` script lets you do this.
# Example Uses
## remapping /bin/sh
On Debian, `/bin/sh` points to `dash`. Maybe you would rather it
point to `bash`.
$ ls -lha /bin/sh
lrwxr-xr-x 1 root root 4 Jun 5 04:08 /bin/sh -> dash
$ remap /bin/sh /bin/bash -- ls -lha /bin/sh
-rwxr-xr-x 1 root root 1,2M 20 oct. 12:53 /bin/sh
## remapping python3
Perhaps you've want to use a python package that requires a python
feature that your distro does not yet support. Compiling this custom
python3 can be a little annoying, because `./configure` makes you
specify where all the various libraries are. It's much easier to just
remap.
$ remap /usr/bin/python3 $HOME/bin/python3-custom -- ./configure
$ remap /usr/bin/python3 $HOME/bin/python3-custom -- cool-package
## Run a command through a custom pflocal
<!-- https://lists.debian.org/debian-hurd/2016/08/msg00016.html -->
$ cd /tmp
$ settrans -ac 1 ~/HURD-SRC/pflocal/pflocal
$ remap /servers/socket/1 /tmp/1 -- /bin/bash -c 'echo huhu world | wc'
1 2 11
## Remapping `/servers/socket/2` and `26` for vpn/firewall
TODO add an example here.
## Use remap to debug lwip
Suppose, you want to debug [[lwip|hurd/lwip]]. You could set `lwip`
on `/servers/socket/2`, but it's hard to use an OS, if your network is
buggy. It would be nice to use the stable `pfinet` and test `lwip` as
needed. You can use the `eth-multiplexer` combined with `remap` to
have such a configuration. First, use the `eth-multiplexer` to change
`pfinet`'s interface from `/dev/eth0` to `/dev/eth0m/0`
# settrans -c /dev/eth0m /hurd/eth-multiplexer --interface=/dev/eth0
Now we configure own main Hurd system to use a virtual network
interface (e.g. `/dev/eth0m/0`) instead. On Debian/Hurd, this can be
accomplished using
# ifdown /dev/eth0
# sed -i -e s_/dev/eth0_/dev/eth0m/0_ /etc/network/interfaces
# ifup /dev/eth0m/0
Then you can do set up `lwip` on `~/lwip/servers/socket{2,26}`
<!-- $ settrans -ac my2 path/to/my-ipstack -what -ever; -->
$ settrans -c ~/lwip/servers/socket/2 /hurd/lwip -i \
/dev/eth0m/1 -4 ~/lwip/servers/socket/2 \
-6 ~/lwip/servers/socket/26
$ settrans -c ~/lwip/servers/socket/26 /hurd/lwip -i \
/dev/eth0m/1 -4 ~/lwip/servers/socket/2 \
-6 ~/lwip/servers/socket/26
$ remap /servers/socket/2 ~/lwip/servers/socket/2 -- \
ping -c 3 gnu.org
If you are running the Hurd in qemu, then you can skip setting up the
`eth-multiplexer` and just configure another virtual ethernet
interface: `eth1`. Then using `lwip` is as simple as:
$ settrans -c ~/lwip/servers/socket/2 -i /dev/eth1 \
-4 ~/lwip/servers/socket/2 -6 ~/lwip/servers/socket/26
$ settrans -c ~/lwip/servers/socket/26 -i /dev/eth1 \
-4 ~/lwip/servers/socket/2 -6 ~/lwip/servers/socket/26
$ remap /servers/socket/2 $HOME/lwip/servers/socket/2 \
-- ping -c 3 gnu.org
Alternatively, you could also launch a subhurd whose's networking uses
lwip. The [[subhurd]] page should give you an idea of how to do this.
## remap example bugs
Remap is written in a rather simplistic way. It should layer over the
filesystem in a better. These examples demonstrate some problems.
$ remap /etc/motd /dev/null -- sh -c 'wc /etc/motd; cd /etc; wc motd;'
0 0 0 /etc/motd
7 40 284 motd
$ settrans $HOME/foo /hurd/remap /bin/sh /bin/bash
$ ls $HOME/foo/
ls: cannot open directory 'foo/': Permission denied
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