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Recently I tried to update time on the server and there was no way to use ntpdate because it was blocked and update raised the following error:
<p>ntpdate pool.ntp.org 6 Nov 21:18:08 ntpdate[23312]: no server suitable for synchronization found</p>
I used this trick to workaround the issue:
date; date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 | grep Date: | cut -d' ' -f5-8)Z"; date Working with many docker containers on one machine I needed to get list of free IP addresses in specific docker network. This is the way:
comm -3 <(nmap -sL 172.30.0.10/29 | awk '/Nmap scan report/{print $NF}' | sort) <(nmap -sn 172.30.0.10/29 | awk '/Nmap scan report/{print $NF}' | sort) | sort -V
172.30.0.9
172.30.0.10
172.30.0.11
172.30.0.12
172.30.0.13
172.30.0.14
172.30.0.15
Let me explain.
This generates the list of IPs in subnetwork:
nmap -sL 172.30.0.10/29 | awk '/Nmap scan report/{print $NF}'
172.30.0.8
172.30.0.9
172.30.0.10
172.30.0.11
172.30.0.12
172.30.0.13
172.30.0.14
172.30.0.15
This generates list of used IPs in subnetwork:
nmap -sn 172.30.0.10/29 | awk '/Nmap scan report/{print $NF}'
172.30.0.8
The comm compares two lists and suppress common lines
comm - compare two sorted files line by line
-3 suppress column 3 (lines that appear in both files)
One more example:
cat ip_pool.txt 172.30.0.8 172.30.0.9 172.30.0.10 172.30.0.11 172.30.0.12 172.30.0.13 172.30.0.14 172.30.0.15 cat ip_used.txt 172.30.0.8 172.30.0.10 comm -3 <(cat ip_pool.txt | sort) <(cat ip_used.txt | sort) | sort -V 172.30.0.9 172.30.0.11 172.30.0.12 172.30.0.13 172.30.0.14 172.30.0.15
On one of slaves I got error:
write failed: No space left on device (28)
I also found that slave got 1062 error (“Duplicate entry”) and stopped. I cleaned up some free space (old logs). When I tried to restart it with pt-slave-restart then I found that IO_Thread downloads binlogs from master and uses all free space again.
As a workaround – I decide to start just SQL_Thread, let it process all relay logs and then start IO_Thread again.
This is quick bash oneliner I created, which checks replication and if 1062 error exists then does skipping and starting SQL_Thread again.
while true; do if [[ $(mysql -e "show slave status\G" | grep "Last_SQL_Errno: 1062" -c) -gt 0 ]]; then mysql -e "set global sql_slave_skip_counter=1; start slave sql_thread;"; fi; done
This was enough to get issue fixed.
How to clear all iptables rules and allow everything
iptables -F iptables -X iptables -t nat -F iptables -t nat -X iptables -t mangle -F iptables -t mangle -X iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT
By default containers are limited to size 10G. I needed to increase container size. For this I added option to file /etc/docker/daemon.json:
{"storage-driver": "overlay"}
After this I restarted docker. Each container now gets total amount of space available on the mount point.
Clean up docker’s images and containers
docker system prune -a -f
Today I needed to clear history from some command. I looked into history and used grep to filtering command I needed.
for i in $(history | grep something | grep -oE "[0-9]{1,} " | sort -rn); do history -d ${i}; done
nmap -sU -p PORT IP
For example Galera requires 4567/udp port opened and I needed to check if it’s opened on one of the nodes.
root@host:~# nmap -sU -p 4567 10.10.20.20 Starting Nmap 7.01 ( https://nmap.org ) at 2018-02-04 10:04 UTC Nmap scan report for 10.10.20.20 Host is up (0.00043s latency). PORT STATE SERVICE 4567/udp closed unknown MAC Address: AB:AB:AB:AB:AB:AB (Unknown) Nmap done: 1 IP address (1 host up) scanned in 0.52 seconds
Dump of all routines of MySQL:
mysqldump --routines --no-create-info --no-data --no-create-db --skip-opt --all-databases > `hostname -s`_stored_procedures.sql
Just found this script. It allows to output grants in graceful way:
mysql -B -N $@ -e "SELECT DISTINCT CONCAT(
'SHOW GRANTS FOR \'', user, '\'@\'', host, '\';'
) AS query FROM mysql.user" | \
mysql $@ | \
sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/## \1 ##/;/##/{x;p;x;}'