NZ Tik

Why won't react re-render on state change?

2019-08-15T22:01:00.000+12:00

If you mutate the state directly it won't re-render.

Instead of...

[cart, setCart] = useState([1,2,3])

const updateCart = (item) => {

prevCart = cart
prevCart.push(item)
setCart(prevCart)

}

Do this....

const updateCart = (item) => {
let prevCart = []
cart.forEach(item => {
prevCart.push(item)
});
setCart(prevCart)

}

Backup dockerized mongodb

2019-08-05T14:06:00.002+12:00

### Backup mongo db container on docker host

```

docker run --rm --network [network] --link [db_container]:mongo -v /Users/sam/db_backups:/backup mongo bash -c 'mongodump -u [username] -p [password] --out /backup --host mongo:27017'

```

### Restore mongodb database

```

docker run --rm --network [network] --link [db_container]:mongo -v /Users/sam/db_backups:/backup mongo bash -c 'mongorestore -u [mong_username] -p [mong_password] /backup --host mongo:27017'

```

The restore will wipe everything that existed before-hand.

Attach existing volume to container with docker-compose

2019-08-05T09:33:00.000+12:00

`docker volume create my_vol`

in docker-compose.yml, declare volumes with property `external: true`. This tells docker compose not to create volumes.

If external = false, then docker compose will prefix the volume declared with the directory name.

Example:

/home
/sam
/docker
/my_app
- docker-compose.yml

The volume name will end up being `my_app_my_vol`

Example docker-compose.yml:

```
version: "3"
volumes:
my_vol:
external: true

services:
my_app:
volumes:
- my_vol:/data <-- attach volume to /data inside container

...
...

```

How to remove stale vcenter licenses

2014-07-25T15:28:00.001+12:00

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2054008

Setup net-snmp on Ubuntu 12.04

2014-03-12T10:32:00.000+13:00

This is the bare minimum to set up snmp on Ubuntu to allow monitoring from Cacti or similar

apt-get update

apt-get install snmpd snmp-mibs-downloader

snmpconf

- Choose /etc/snmp/snmpd.conf
- Choose snmpd.conf
- Choose 3 for 'Access Control'
- Choose 3 for RO community
- Type community name
- Press enter or type allowed network/host
- Press enter to allow all OID

mv snmpd.conf /etc/snmp/

service snmpd restart

IPTables example

2014-02-19T15:50:00.001+13:00

Allow tcp port 80 from source address 192.168.10/24
iptables -A INPUT -i 10 -P TCP -S 192.168.1.0/24 --dport 80 -j ACCEPT

Drop tcp port 80 from range of addresses
iptables -A INPUT -i 10 -p tcp --dport 80 -m iprange --src-range 192.168.1.1-192.168.1.254 -j DROP

List chain with rule numbers
iptables -nL INPUT -v --line-numbers

Delete particular rule
iptables -D INPUT 10

DHCP option 121

2013-12-18T11:14:00.000+13:00

http://tools.ietf.org/html/rfc3442

This is used to add a classless static route to the DHCP clients.

To add option 121 to a Mikrotik DHCP server, it's value is specified in HEX. The format is as follows.

0xnnddddddddgggggggg

where n=mask, d=destination, g=gateway.

To convert ip address to HEX, you convert each octet, so 192=C0, 168=A8, 55=37, 1=01

You can use a tool such as http://www.miniwebtool.com/ip-address-to-hex-converter/?ip=192.168.55.1

Example:

To add a route to the destination network of 192.168.55.0/24 via gateway 172.16.10.1.

/ip dhcp-server option add name=classlessroutes code=121 value=0x18C0A837AC100A01

where 18 is 24 in hex.

*note: depending on the subnet mask, you may only need to specify 0-4 octets. In fact only the non-zero, or network portion of the subnet. Here is a table from the RFC.

             subnet mask           Number of octets
                     0                        0
                  1- 8                       1
                  9-16                      2
                 17-24                     3
                 25-32                     4

so for the /24 subnet in the above example, we only needed to specify 3 octets - C0A837

Mikrotik Bridge Horizon

2013-11-02T20:54:00.000+13:00

To achieve similar functionality to Cisco's private VLANS, where all ports are on the same L2 segment, but cannot exchange packets, you can use Mikrotik's Bridge Horizon feature.

Basically, every port in a bridge is assigned a horizon value, and RouterOS will only forward frames to other interfaces in the bridge that have different horizon values.

This means that you assign the same horizon value to the interfaces that you don't want to be able to communicate.

For example, you want to bridge all your customers and use a single /24 subnet and the same gateway. Typically this is bad and poses a huge security risk, not to mention performance issues. If you assign the same horizon value to the customer interfaces, then the router will not forward traffic between customers. Customer A will not be able to ping Customer B.

If you had a server, such as an IP-PBX that all customers needed to access, and you were lazy and added it to the bridge, then you would assign a different horizon value to that port.

mysql timezones

2013-10-21T13:46:00.000+13:00

Add the timezone names to the mysql table:

root@db1:~# mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root

mysql> CONVERT_TZ( 'datetime', 'from_timezone', 'to_timezone')

Mikrotik NAT, access services via external IP from inside the network

2013-09-26T11:17:00.000+12:00

The laptop at 192.168.1.10 wants to communicate with the web server on 192.168.1.10 via the external IP address of the Mikrotik router at 1.1.1.1.

Say you have a service such as webmail, which has a nat rule to allow access from an external network...

/ip firewall nat add chain=dstnat action=dst-nat dst-address=1.1.1.1 protocol=tcp dst-port=888 to-port=80 to-address=192.168.1.10

This works fine of course, so users set up the shortcut to http://1.1.1.1:888

Problem is when they are on the internal network it doesn't work, because the Mikrotik router won't send the reply data back out the same interface. A work-around is to create a src-nat rule directly below the dst-nat rule like this.

/ip firewall nat add chain=srcnat action=masquerade src-address=192.168.1.0/24 dst-address=192.168.1.10

Goes something like this..

1. Client initiates http request to 1.1.1.1:888
2. MT receives and translates destination to 192.168.1.10 as per 1st rule
3. MT then translates the src address from 192.168.1.160 to 192.168.1.1 as per 2nd rule
4. Now communication appears to be between 192.168.1.160 and 192.168.1.1

Happy days.

Export from LDAP with ldapsearch example

2013-03-11T12:41:00.003+13:00

This does an unauthenticated bind and exports the Framed IP Address from OpenLDAP

'-x' simple, no SASL
'-D' bind as
'-w' password
'-b' search base (starting point)
'-s sub' search sub tree

ldapsearch -x -LLL -D 'cn=admin,dc=domain,dc=net' -w password -b 'ou=users,dc=domain,dc=net' -s sub radiusFramedIPAddress >> /var/tmp/radiusUsers.txt

Mikrotik Dot Q-in-Q

2012-09-10T10:57:00.001+12:00

How to create a Q-in-Q or 802.1ad double-tagged interface on a Mikrotik Router:

Stripped down 802.1ad packet:

DST-MAC | SRC-MAC | 802.1Q outer | 802.1Q inner | PAYLOAD

/interface vlan
add interface=ether1 name=outervlan vlan-id=600
add interface=outervlan name=innervlan vlanid=1500

The router will strip the outer vlan tag to expose the inner vlan. vlan 1500 is essentially tunnelled using the outer vlan (600) across the provider network.

MPLS Routing Loop

2012-06-26T15:00:00.000+12:00

Certain destination IP addresses are not routable within certain parts of the network, and appear to loop. This has been narrowed down to the label swap on a Cisco 6500 for the next hop of a GRE tunnel [point2point].

As per the LFIB, the Cisco 6500 is appending label 133 for network 10.10.32.1 and sending it out tun0, but appears to be snatching the packet back again, as it has a local label of 133 for the network 10.10.32.70/32.

##Traceroute from test router (simplified for readability)

10.10.64.220 and 10.8.8.2 are c6500 interfaces, the latter being the GRE interface.

[admin@rtr3] > /tool trace 10.10.32.1
# ADDRESS STATUS
1 10.10.32.137 <MPLS:L=873,E=0> **local-label for 10.10.32.1
2 10.10.64.220 <MPLS:L=71,E=0> **local-label for 10.10.32.1
**appends label 133 as per LFIB

3 10.8.8.2 <MPLS:L=133,E=0> **takes the packet back as per LIB
4 10.10.64.214 <MPLS:L=218,E=0> **appends label for 10.10.32.70
5 10.10.64.135 <MPLS:L=422,E=0> **pops label
6 10.10.64.66 **reads original ip header and appends
label for 10.10.32.1
7 10.10.64.67 <MPLS:L=1032,E=0> **
8 10.10.64.134 <MPLS:L=835,E=0> **
9 10.10.64.220 <MPLS:L=71,E=0> ** and carries on until the TTL expires

#show mpls ldp bindings local-label 71
lib entry: 10.10.32.1/32, rev 1474
local binding: label: 71

#show mpls ldp bindings local-label 133
lib entry: 10.10.32.70/32, rev 636
local binding: label: 133

#show mpls forwarding-table labels 71
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
71 133 10.10.32.1/32 22346897 Tu0 point2point

No routing loops occur when the router preceeding the c6500 pops the label. This is obviously due to using the routing table.

Possible solutions perhaps specify next hop IP for the label rather than the p2p interface, somehow preventing local labels from having the same labels as the remote gre end point.

I believe if I rebuild the LFIB, this problem will go away... until next time. I would like to find a solution, whether it be a bug fix or best practice, or perhaps something that I am missing or haven't RTFM'd properly.

BIND DNS server slave config on ubuntu

2012-05-17T17:06:00.001+12:00

apt-get update
apt-get install bind9

Edit named.conf.options as usual.

Edit named.conf.local and add zone

zone "test.net" {
type slave;
file "db.test.net";
masters { 172.16.99.200; };
};

where 172.16.99.200 is the master DNS server. The above relative syntax of the file will be /var/cache/bind/*. If you want to specify a particular location such as...

zone "test.net" {

type slave;

file "/etc/bind/zones/db.test.net";

masters { 172.16.99.200; };

};

...then you may need to modify permissions as well as apparmour to allow writing to the directory.

chown -R root:bind /etc/bind/zones

chmod -R 770 /etc/bind/zones

nano /etc/apparmor.d/usr.sbin.named

add this line somewhere:

/etc/bind/slave/* rw,

/etc/init.d/bind9 restart on the slave and check the zone directory to see if populated. If not tail -f /var/log/syslog will help troubleshoot.

Link Nagios to root of website

2012-04-23T14:33:00.000+12:00

By default nagios is accessible at http://nagiosserver/nagios3. To have it accessible at http://nagiosserver, link the htdocs and stylesheet to /var/www (or wherever the root is located).

rm -r /var/www
ln -s /usr/share/nagios3/htdocs/ /var/www
ln -s /etc/nagios3/stylesheets /var/www

You can change /var/www to /var/www/whateever, so that it is accessible at http://nagiosserver/whatver

VMWare ESX tools install on Ubuntu

2012-04-18T14:25:00.002+12:00

This is to install the open vm tools, which works on all Ubuntu distributions I have tried.

apt-get update
apt-get install linux-headers-virtual
apt-get install --no-install-recommends open-vm-dkms
apt-get install --no-install-recommends open-vm-tools

How to tell if Linux kernel is 32 or 64bit

2012-04-16T12:33:00.002+12:00

uname -m

#32 bit
i686

#64bit
x86_64

Make tftpd-hpa play nicely with Cisco

2012-04-05T11:07:00.001+12:00

The following was tested on Ubuntu 11.10. This is completely insecure, make sure it is confined to a LAN environment, i.e. not publicly accessibly.

apt-get install tftpd-hpa

mkdir /tftp

chmod 777 /tftp

nano /etc/default/tftpd-hpa

# /etc/default/tftpd-hpa
TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/tftp"
TFTP_ADDRESS="0.0.0.0:69"
TFTP_OPTIONS="--secure --create -v"

service tftpd-hpa restart

--create is needed to allow client to create new file. Otherwise you will get error stating 'File does not exist' or similar.

--secure is so that the client does not need to specify an absolute path such as /tftp/file. The root of the tftp server becomes TFTP_DIRECTORY.

-v is for verbose logging in /var/syslog

culv-lns1#copy run tftp
Address or name of remote host []? 10.2.2.40
Destination filename [culv-lns1-confg]?
!!
1446 bytes copied in 0.168 secs (8607 bytes/sec)
_________________________________________________

culv-lns1#copy tftp://10.2.2.40/test.0 flash
Destination filename [test.0]?
Accessing tftp:// 10.2.2.40 /test.0...
Loading test.0 from 10.2.2.40 (via GigabitEthernet0/0): !
[OK - 816 bytes]

816 bytes copied in 0.408 secs (2000 bytes/sec)

Backup OpenLDAP Ubuntu

2012-02-21T11:58:00.000+13:00

The default database location is /usr/lib/ldap

It is recommended to backup to LDIF so it is transportable. Use slapcat to export.

slapcat -v -l /backups/ldapbackup.ldif

To restore use slapadd.

cd /usr/lib/ldap
rm *
slapadd -l ldapbackup.ldif

-v is verbose output
-l specifies the ldif format

nagios bash: ./check_disk: No such file or directory [UBUNTU]

2012-02-14T14:18:00.000+13:00

Reminder: Install plugins with apt-get install nagios-plugins rather than copying from another server.

May have been missing an interpreter or something.

Delete Files Older Than x Days

2012-02-14T09:57:00.000+13:00

Applies to FreeBSD and Linux.

/mnt
/backup1
/server1
/folder1
/folder2
/backup1.tar.gz
/server2
/server3

find /mnt/backup1 -maxdepth 2 -name '*.gz' -mtime +7 -exec rm {} \;

This will find and remove files that are 7 days old. It will search 2 folders deep from /mnt/backup1. It will not search folder1 or folder2. The single quotes around the name search string are required at least on FreeBSD.

HP SNMP agents and Ubuntu

2012-02-03T16:43:00.003+13:00

This will allow you to monitor HP hardware, i.e. RAID controller, degraded disk etc. This was done on Ubuntu 10.04

wget http://downloads.linux.hp.com/SDR/downloads/bootstrap.sh
chmod +x bootstrap.sh
./bootstrap.sh -r ProLiantSupportPack (this adds the HP repo to apt's sources)
wget http://downloads.linux.hp.com/SDR/downloads/ProLiantSupportPack/GPG-KEY-ProLiantSupportPack
apt-key add GPG-KEY-ProLiantSupportPack
aptitude update
apt-get install hp-snmp-agents

apt-get install net-snmp (or apt-get install snmp for later versions)

/sbin/hpsnmpconfig - Follow the prompts

nano /etc/default/snmpd

#modify this line, replacing x.x.x.x with your public facing IP if needed

SNMPDOPTS='-Lsd -Lf /dev/null -u snmp -g snmp -I -smux -p /var/run/snmpd.pid 127.0.0.1 x.x.x.x'

##########################################

Restart snmp
/etc/init.d/snmpd restart

Start the agents!

/etc/init.d/hp-snmp-agents start

Test with

snmpwalk -v 1 -c rocom localhost 1.3.6.1.4.1.232

Display PHP errors on web page

2012-01-12T09:58:00.005+13:00

So you don't have to troll logs when your web page doesn't display what is expected, copy and paste this to the top of your PHP code.

ini_set('display_errors', 1);
ini_set('log_errors', 1);
ini_set('error_log', dirname(__FILE__) . '/error_log.txt');
error_reporting(E_ALL);

You will probably want to remove it once in production.

Mikrotik For Loop

2011-12-21T09:09:00.000+13:00

maori port scan.

:for p from=20 to=80 do={:put $p;/system telnet 10.32.99.166 $p}

rsync example

2011-11-14T20:37:00.001+13:00

The -u switch in rsync does not work between different file systems so it seems. It is supposed to ignore existing files in the destination directory, but it doesn't - well at least it doesn't between UFS and EXT3 in my doings.

Using the --size-only switch along side -u is a work around.

Example rsync for my reference:

rsync -airu --size-only /source/dir /dest/dir

-a archive mode
-i itemise change summary
-r recursive
-u ignore existing files

man rsync