sargun

root@ubuntu:~# echo $$
4249
# Switched back to initial namespace session
sargun@ubuntu:~$ ps u 4249
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
sargun      4249  0.1  0.1  15184  8704 pts/0    S+   20:51   0:00 -bash
sargun@ubuntu:~$ hostname
ubuntu

sargun

sargun@ubuntu:~$ capsh --decode=$(gawk -F':\t+' '$1 == "CapEff" { print $2; }' /proc/$$/status)
0x0000000000000000=

sargun

root@ubuntu:~# capsh --decode=$(gawk -F':\t+' '$1 == "CapEff" { print $2; }' /proc/self/status) 
0x000001ffffffffff=cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read,38,39,40

sargun

root@ubuntu:~# strace -e trace=unshare -e 'signal=!all' unshare --uts
unshare(CLONE_NEWUTS)                   = 0
root@ubuntu:~# strace -e trace=sethostname -e 'signal=!all' hostname foo
sethostname("foo", 3)                   = 0
+++ exited with 0 +++
root@ubuntu:~# 
root@ubuntu:~# hostname
foo

sargun

root@ubuntu:~# strace -e trace=sethostname -e 'signal=!all' hostname foo
sethostname("foo", 3)                   = -1 EPERM (Operation not permitted)
hostname: you must be root to change the host name
+++ exited with 1 +++

sargun

sargun@ubuntu:~$ id
uid=1000(sargun) gid=1000(sargun) groups=1000(sargun),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),110(lxd),115(lpadmin),116(sambashare),139(wireshark),999(docker)
sargun@ubuntu:~$ strace -e trace=sethostname hostname foo
sethostname("foo", 3)                   = -1 EPERM (Operation not permitted)
hostname: you must be root to change the host name
+++ exited with 1 +++

sargun

root@ubuntu:~# capsh --print
WARNING: libcap needs an update (cap=40 should have a name).
Current: =ep
Bounding set =cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read,38,39,40
Ambient set =
Securebits: 00/0x0/1'b0
 secure-noroot: no (unlocked)
 secure-no-suid-fixup: no (unlocked)
 secure-keep-caps: no (unlocked)

sargun

root@ubuntu:~# unshare -u
root@ubuntu:~# hostname foo
root@ubuntu:~# hostname
foo

sargun

root@ubuntu:~# unshare -u
root@ubuntu:~# hostname foo
root@ubuntu:~# 

sargun

root@ubuntu:~# hostname foo
hostname: you must be root to change the host name