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These 15 lines of bash will start a container running the fish shell. Try it! (download this script at bit.ly/containers-arent-magic)
It only runs on Linux because these features are all Linux-only.
wget bit.ly/fish-container -O fish.tar (# 1. download the image)
mkdir container-root; cd container-root
tar -xf ../fish.tar (# 2. unpack image into a directory)
cgroup_id="cgroup_$(shuf -i 1000-2000 -n 1)" (# 3. generate random cgroup name)
cgcreate -g "cpu, cpuacct, memory: $cgroup_id" (# 4. make a cgroup & set CPU/memory limits)
cgset -r cpu. shares=512 "$cgroup_id"
cgset -r memory.limit_in_bytes=1000000000 \
"$cgroup_id"
cgexec -g "cpu, cpuacct, memory: $cgroup_id" \ (# 5. use the cgroup)
unshare -fmuipn --mount-proc\ (# 6. make and use some namespaces)
chroot "$PWD" \ (# 7. change root directory)
/bin/sh -c "
/bin/mount -t proc proc /proc && (# 8. use the right /proc)
hostname container-fun-times && (# 9. change the hostname)
/usr/bin/fish" (# 10. finally, start fish!)