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Ci-dessous, les différences entre deux révisions de la page.

--- tech:notes_ipc [2025/03/24 15:06] – créée - modification externe 127.0.0.1
+++ tech:notes_ipc [2026/06/07 19:12] (Version actuelle) – modification externe 127.0.0.1
@@ Ligne 1: / Ligne 1: @@
+<!DOCTYPE markdown>
+{{tag>Brouillon Hardware CPU}}
+# Notes IPC shared memory
+Voir :
+* http://tvaira.free.fr/bts-sn/multitache/cours-multitache-3.pdf
+* https://www.youtube.com/watch?v=9OZofG500Js  Processus et Sémaphores Chaker El Amrani
+* https://gerardnico.com/linux/shared_memory
+* http://www.thegeekstuff.com/2010/08/ipcs-command-examples/
+* http://www.postgresql.org/docs/current/static/kernel-resources.html
+* http://www.postgresql.org/docs/9.1/static/kernel-resources.html#SYSVIPC
+* http://sysnet-adventures.blogspot.com/2014/02/omreport-fails-object-not-found.html
+* http://brunogarcia.chez.com/Unix/Docs/IPC.html
+* `ipcrm` / `ipcmk`
+Voir aussi :
+* https://fr.wikipedia.org/wiki/Situation_de_comp%C3%A9tition
+~~~bash
+#Total de la RAM
+total=$(cat /proc/meminfo | grep MemTotal | awk '{print $2}')
+# 90% de la mémoire physique max
+ratio=0.9
+# On applique le ratio et on converti en pages de 4096
+shmall=$(echo $total/4096*$ratio+1 | bc)
+shmmax=$(echo $total*$ratio | bc)
+# On arrondi la valeur
+shmall=$(echo $shmall | sed -e 's/\..*$//')
+shmmax=$(echo $shmmax | sed -e 's/\..*$//')
+echo $shmall > /proc/sys/kernel/shmall
+echo $shmmax > /proc/sys/kernel/shmmax
+# ipcs -lm
+#################
+#################
+# Overcommit memory ?
+# sysctl -w vm.overcommit_memory=2
+# Page size ?
+# getconf PAGE_SIZE
+# cat /proc/sys/kernel/shmmni
+#################
+#### SEMAPHORES
+# http://www.postgresql.org/docs/9.1/static/runtime-config-connection.html#GUC-MAX-CONNECTIONS
+# SEMMNS is the second parameter in output of cat /proc/sys/kernel/sem (default value 32000)
+# SEMMNI is the last parameter there, default value 128 - this is the limiting factor - SEMMNI must be at least at least ceil(max_connections / 16)
+# http://www.puschitz.com/TuningLinuxForOracle.shtml#TheSEMMNSParameter
+# http://www.postgresql.org.es/node/229
+####
+~~~
+Connaître la PAGE_SIZE \\
+Voir https://en.wikipedia.org/wiki/Page_%28computer_memory%29
+~~~bash
+getconf PAGE_SIZE
+cat /proc/sys/kernel/shmmni
+~~~
+~~~
+$ ipcs
+------ Message Queues --------
+key        msqid      owner      perms      used-bytes   messages
+------ Shared Memory Segments --------
+key        shmid      owner      perms      bytes      nattch     status
+x0052e2c1 32768      postgres   600        56         20
+x00000000 17924097   wouter     600        33554432   2          dest
+x00000000 49446914   wouter     600        524288     2          dest
+[...]
+$ ipcs -i 17924097 -m -p
+Shared memory Segment shmid=17924097
+uid=1000    gid=1000    cuid=1000   cgid=1000
+mode=01600  access_perms=0600
+bytes=33554432  lpid=3808   cpid=1457   nattch=2
+att_time=Fri Jul  3 10:43:28 2015
+det_time=Fri Jul  3 10:43:28 2015
+change_time=Fri Jul  3 10:03:00 2015
+~~~
+## Debug
+Source : http://www.makelinux.net/alp/035
+The ipcs command provides information on interprocess communication facilities, including shared segments. Use the -m flag to obtain information about shared memory. For example, this code illustrates that one shared memory segment, numbered 1627649, is in use:
+~~~
+% ipcs -m
+------ Shared Memory Segments -------
+key       shmid     owner     perms     bytes     nattch    status
+x00000000 1627649   user    640       25600     0
+~~~
+If this memory segment was erroneously left behind by a program, you can use the ipcrm command to remove it.
+~~~
+% ipcrm shm 1627649
+~~~
+Periodically remove allocated semaphores which belong to the user running the plugin. This can be achieved like this (example for the user "nrpe")\\
+Source : http://folk.uio.no/trondham/software/check_openmanage.html
+~~~bash
+ipcrm $(ipcs -s | awk '/nrpe/ {print "-s ",$2}')
+~~~