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linux_wiki:command_many_systems_part1_basics [2016/11/28 22:50] 127.0.0.1 external edit |
linux_wiki:command_many_systems_part1_basics [2019/05/25 23:50] |
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| - | ====== Execute Commands on Many Systems ====== | ||
| - | |||
| - | **General Information** | ||
| - | |||
| - | Different methods to manipulate a large amount of systems. | ||
| - | |||
| - | **Checklist** | ||
| - | * Distro(s): Any | ||
| - | * Other: Use of [[linux_wiki: | ||
| - | |||
| - | ---- | ||
| - | |||
| - | ====== Systems in Serial ====== | ||
| - | |||
| - | For some things, it is better to do a rolling serial change...such as restarting a web server. | ||
| - | |||
| - | This example restarts the Apache webserver on a list of systems serially, and sleeps 10 seconds in between each. | ||
| - | |||
| - | 1) Populate a text file with the list of systems, one per line. Example: | ||
| - | |||
| - | host_list.txt | ||
| - | < | ||
| - | webserver01 | ||
| - | webserver02 | ||
| - | webserver03 | ||
| - | ... | ||
| - | </ | ||
| - | |||
| - | 2) Execute a for loop through that list: | ||
| - | <code bash> | ||
| - | for NODE in $(cat host_list.txt) | ||
| - | do echo -e " | ||
| - | ssh admin@${NODE} ' | ||
| - | echo "---- Done with ${NODE} ----" | ||
| - | sleep 10 | ||
| - | done | ||
| - | </ | ||
| - | |||
| - | ---- | ||
| - | |||
| - | ====== Systems in Parallel ====== | ||
| - | |||
| - | If you would rather get something done very quickly, commands can be sent in parallel. | ||
| - | |||
| - | 1) Create a script that will operate on 1 system. | ||
| - | |||
| - | This script takes 1 argument; a system hostname. | ||
| - | <code bash single_host.sh> | ||
| - | #!/bin/bash | ||
| - | |||
| - | HOST=$1 | ||
| - | echo " | ||
| - | ssh admin@${HOST} ' | ||
| - | </ | ||
| - | |||
| - | 2) Create a script that will call that script. | ||
| - | |||
| - | This script takes two+ arguments: | ||
| - | * Max Number of forks | ||
| - | * Hostnames (space seperated) | ||
| - | <code bash parallel_hosts.sh> | ||
| - | #!/bin/bash | ||
| - | |||
| - | MAX_FORKS=$1 | ||
| - | shift | ||
| - | FORKS=0 | ||
| - | |||
| - | for HOST in $@; do | ||
| - | if [ ${FORKS} -ge ${MAX_FORKS} ]; then | ||
| - | wait | ||
| - | FORKS=0 | ||
| - | fi | ||
| - | (single_host.sh ${HOST}) & | ||
| - | FORKS=$(( ${FORKS} + 1 )) | ||
| - | done | ||
| - | wait | ||
| - | </ | ||
| - | |||
| - | 3) Call the parallel_hosts.sh script. | ||
| - | |||
| - | In this example, parallel_hosts.sh will spawn a max of 10 processes at a time: | ||
| - | <code bash> | ||
| - | parallel_hosts.sh 10 $(cat host_list.txt) | ||
| - | </ | ||
| - | |||
| - | ===== Parallel Explanation ===== | ||
| - | |||
| - | * parallel_hosts.sh is called with two arguments: 10 and an expanded list of host names | ||
| - | * The first argument (10) is assigned to MAX_FORKS | ||
| - | * shift (with no number) moves all arguments down a position, so the 10 drops off, and now $1 is the first host name from the text file. | ||
| - | * The for loop goes through each argument ($@) starting at $1 | ||
| - | * If FORKS is ever equal to the MAX_FORKS, wait is used to pause until all child processes have completed. | ||
| - | * Otherwise, call single_host.sh ${HOST}, creating a child process and sending it the current host in the loop to execute on. | ||
| - | * Finally, after the loop is complete, a final wait is used to ensure that any other single_host.sh child processes can finish cleanly. | ||
| - | |||
| - | ---- | ||