net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

# ip -6 a
#

# ip -6 addr
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 <censored>/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 2591985sec preferred_lft 604785sec
    inet6 fe80::250:56ff:feae:c158/64 scope link
       valid_lft forever preferred_lft forever

# sysctl net.ipv6.conf.all.disable_ipv6 net.ipv6.conf.default.disable_ipv6 net.ipv6.conf.lo.disable_ipv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

# sysctl -w net.ipv6.conf.all.disable_ipv6=1 net.ipv6.conf.default.disable_ipv6=1 net.ipv6.conf.lo.disable_ipv6=1
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
# ip -6 addr
#

# cat /proc/sys/net/ipv6/conf/all/disable_ipv6
1
# ip -6 a
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 <censored>/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 2591945sec preferred_lft 604745sec
    inet6 fe80::250:56ff:feae:c158/64 scope link
       valid_lft forever preferred_lft forever
# echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
# ip -6 a
#