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Document uid/gidmap are based on subuid/gid mapping

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* Closes #6123

Signed-off-by: Tobias Boesch <tobias.boesch@googlemail.com>
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Tobias Boesch 2020-12-11 22:36:56 +01:00
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docs/source/markdown/podman-run.1.md
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@ -394,6 +394,13 @@ Run the container in a new user namespace using the supplied mapping. This optio
This option can be passed several times to map different ranges. If calling **podman run** as an unprivileged user, the user needs to have the right to use the mapping. See **subuid**(5).
The example maps gids **0-1999** in the container to the gids **30000-31999** on the host: **--gidmap=0:30000:2000**.
**Important note:** The new user namespace mapping based on **--gidmap** is based on the initial mapping made in the _/etc/subgid_ file.
Assuming there is a _/etc/subgid_ mapping **groupname:100000:65536**, then **groupname** is initially mapped to a namespace starting with
gid **100000** for **65536** ids. From here the **--gidmap** mapping to the new namespace starts from **0** again, but is based on the initial mapping.
Meaning **groupname** is initially mapped to gid **100000** which is referenced as **0** in the following **--gidmap** mapping. In terms of the example
above: The group **groupname** is mapped to group **100000** of the initial namespace then the
**30000**st id of this namespace (which is gid 130000 in this namespace) is mapped to container namespace group id **0**. (groupname -> 100000 / 30000 -> 0)
#### **--group-add**=*group*
Add additional groups to run as
@ -1026,6 +1033,15 @@ as an unprivileged user, the user needs to have the right to use the mapping. Se
The following example maps uids 0-1999 in the container to the uids 30000-31999 on the host: **--uidmap=0:30000:2000**.
**Important note:** The new user namespace mapping based on **--uidmap** is based on the initial mapping made in the _/etc/subuid_ file.
Assuming there is a _/etc/subuid_ mapping **username:100000:65536**, then **username** is initially mapped to a namespace starting with
uid **100000** for **65536** ids. From here the **--uidmap** mapping to the new namespace starts from **0** again, but is based on the initial mapping.
Meaning **username** is initially mapped to uid **100000** which is referenced as **0** in the following **--uidmap** mapping. In terms of the example
above: The user **username** is mapped to user **100000** of the initial namespace then the
**30000**st id of this namespace (which is uid 130000 in this namespace) is mapped to container namespace user id **0**. (username -> 100000 / 30000 -> 0)
_Note_: A minimal mapping has to have at least container uid **0** mapped to the parent user namespace.
#### **--ulimit**=*option*
Ulimit options. You can use **host** to copy the current configuration from the host.