操作環境
SuSE11sp1
問題現象
執行su - test命令切換失敗，提示"su: cannot set user id: Resource temporarily unavailable"
問題分析
猜測是test使用資源超過系統的限制（比如進程數、打開的文件句柄）
1、查看/etc/security/limits.conf文件，文件並無對test用戶做特殊限制
2、ulimit -a，查看輸出結果與步驟1中的配置一致。
3、pf -fu test | wc -l，查看test用戶打開的進程數，小於上述通用配置nproc參數值。OK
4、lsof | awk '{print $3}' | sort | uniq -c,查看test用戶打開的文件句柄數。小於上述通用配置的參數值nofile。OK
5、ps -eLF | grep 'test'|wc-l,查看test用戶打開的線程數（Java里面的一個線程在Linux下會最終映射成操作系統的一個進程），等於當前通用配置的參數值nproc。找到了原因。因此需要修改nproc參數。
問題解決
1、調大/etc/security/limits.conf中nproc參數。不需要重啟。
2、執行ulimit -a查看確認修改已生效。
3、重新執行su - test，切換成功。問題解決
知識拓展
1、/etc/security/limits.conf文件及內容介紹
# /etc/security/limits.conf # #This file sets the resource limits for the users logged in via PAM. #It does not affect resource limits of the system services. # #Also note that configuration files in /etc/security/limits.d directory, #which are read in alphabetical order, override the settings in this #file in case the domain is the same or more specific. #That means for example that setting a limit for wildcard domain here #can be overriden with a wildcard setting in a config file in the #subdirectory, but a user specific setting here can be overriden only #with a user specific setting in the subdirectory. # #Each line describes a limit for a user in the form: # #<domain> <type> <item> <value> # #Where: #<domain> can be: # - a user name # - a group name, with @group syntax # - the wildcard *, for default entry # - the wildcard %, can be also used with %group syntax, # for maxlogin limit # #<type> can have the two values: # - "soft" for enforcing the soft limits # - "hard" for enforcing hard limits # #<item> can be one of the following: # - core - limits the core file size (KB) # - data - max data size (KB) # - fsize - maximum filesize (KB) # - memlock - max locked-in-memory address space (KB) # - nofile - max number of open file descriptors # - rss - max resident set size (KB) # - stack - max stack size (KB) # - cpu - max CPU time (MIN) # - nproc - max number of processes # - as - address space limit (KB) # - maxlogins - max number of logins for this user # - maxsyslogins - max number of logins on the system # - priority - the priority to run user process with # - locks - max number of file locks the user can hold # - sigpending - max number of pending signals # - msgqueue - max memory used by POSIX message queues (bytes) # - nice - max nice priority allowed to raise to values: [-20, 19] # - rtprio - max realtime priority # #<domain> <type> <item> <value> # #* soft core 0 #* hard rss 10000 #@student hard nproc 20 #@faculty soft nproc 20 #@faculty hard nproc 50 #ftp hard nproc 0 #@student - maxlogins 4 # End of file @users soft nofile 100001 @users hard nofile 100002 @root soft nofile 100001 @root hard nofile 100002
2、ulimit命令，設置限制,可以把命令加到profile文件里，也可以在/etc/security/limits.conf文件中定義限制。
常用參數如下
-a 顯示所有限制 -n 打開文件數的上限 -u 進程數的上限 -c core文件大小的上限 -d 進程數據段大小的上限 -f shell所能創建的文件大小的上限 -m 駐留內存大小的上限 -s 堆棧大小的上限 -t 每秒可占用的CPU時間上限 -p 管道大小 -v 虛擬內存的上限