1. namespaces
-------------

sudo unshare --fork --pid --mount-proc bash

sudo nsenter -t 30476 -a
sudo nsenter -t 30476 -p -r ps aux

ls -al /proc/<pid>/ns
https://elixir.bootlin.com/linux/latest/source/include/linux/sched.h#L737



The former implementation of gethostname(): 
------------------------------------------
asmlinkage long sys_gethostname(char __user *name, int len) {
..
if (copy_to_user(name, system_utsname.nodename, i)) 
errno = -EFAULT;
}
(system_utsname is a global)
kernel/sys.c, Kernel v2.6.11.5


A new method called utsname() added: 
-----------------------------------

static inline struct new_utsname *utsname(void)
{
return &current->nsproxy->uts_ns->name;
}

The new implementation of gethostname(): 
SYSCALL_DEFINE2(gethostname, char __user *, name, int, len) {
struct new_utsname *u;
...
u = utsname();
if (copy_to_user(name, u->nodename, i))
errno = -EFAULT;


------- hostname example

puru@synerg:~$ 
puru@synerg:~$ sudo unshare --fork --pid --mount-proc bash
[sudo] password for puru: 
root@synerg:~# hostname
synerg
root@synerg:~# hostname newsynerg
root@synerg:~# hostname
newsynerg
root@synerg:~# exit
puru@synerg:~$ sudo unshare --fork -u --pid --mount-proc bash
root@synerg:~# hostname newsynerg
root@synerg:~# hostname
newsynerg
root@synerg:~# 


2.  cgroups
-----------

/proc/cgroups
/proc/<pid>/cgroup     /* cgroup information */

ls -al /sys/fs/cgroup/ /* cgroup operations interaction, cgroup controllers */ 





mkdir /sys/fs/cgroup/memory/mygroup
echo $$ > /sys/fs/cgroup/memory/mygroup/tasks
echo 1M > /sys/fs/cgroup/memory/mygroup/memory.limit_in_bytes
echo 1 > /sys/fs/cgroup/memory/mygroup/memory.oom_control
~puru/temp/a.out
echo 0 > /sys/fs/cgroup/memory/mygroup/memory.oom_control


do_exit
https://elixir.bootlin.com/linux/latest/source/kernel/exit.c#L805
cgroup_exit
https://elixir.bootlin.com/linux/latest/source/kernel/cgroup/cgroup.c#L6662
struct css_set
https://elixir.bootlin.com/linux/latest/source/include/linux/cgroup-defs.h#L212
*cgroups
https://elixir.bootlin.com/linux/latest/source/include/linux/sched.h#L1221



3. chroot + images

chroot /home/puru/temp/ bash
ldd /bin/bash 
cp /lib/x86_64-linux-gnu/libtinfo.so.5 /lib/x86_64-linux-gnu/libdl.so.2 /lib/x86_64-linux-gnu/libc.so.6 temp/lib
cp /lib64/ld-linux-x86-64.so.2  temp/lib64/
chroot /home/puru/temp/ bash
ls
ldd /bin/ls
cp /lib/x86_64-linux-gnu/libselinux.so.1 /lib/x86_64-linux-gnu/libc.so.6 /lib/x86_64-linux-gnu/libpcre.so.3  /lib/x86_64-linux-gnu/libdl.so.2 /lib/x86_64-linux-gnu/libpthread.so.0 temp/lib
cp /lib64/ld-linux-x86-64.so.2  temp/lib64
chroot /home/puru/temp/ bash
ls