修改 kernel 参数

# locate grub.cfg             # or grub.conf
# vi /boot/efi/EFI/centos/grub.cfg

ll /etc/rc.local
chmod +x /etc/rc.d/rc.local
vi /etc/rc.local                  # 追加以下两行内容
echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo never > /sys/kernel/mm/transparent_hugepage/defrag

修改系统变量

查看kernel参数

                                                                   # 每个进程可以打开的最大文件数
sysctl -A  | grep fs\.file-max                      # fs.file-max = 764817
sysctl fs.file-max
cat /proc/sys/fs/file-max

vi /etc/sysctl.conf                                      # 修改系统级的配置，持久生效
fs.file-max = 787933

sysctl -p                                                     # 重新加载配置文件，使其即时生效


#  高并发web连接
net.ipv4.tcp_max_syn_backlog = 100000
net.core.somaxconn = 65535
net.ipv4.tcp_syncookies = 0

查看指定进程正在使用的文件数量

ls -la /proc/<pid>/fd
lsof -p <pid of process>
lsof -p <pid> | wc -l
ulimit -n

查看指定用户开启的总进程数

ps auxwwf | grep $USER_NAME | grep -v grep | wc -l

upper limit on inotify watches reached

sudo sysctl fs.inotify.max_user_watches
sudo sysctl fs.inotify.max_user_watches=8192000

sudo vi /etc/sysctl.conf
fs.inotify.max_user_watches=8192000

修改用户限制

vi /etc/pam.d/login                 # 确认已经启用 pam_limits.so
session required pam_limits.so

man limits.conf

ulimit -Ha                          # 检查所有硬限制（比如用户最大进程数、可打开的最大文件数）
ulimit -Sa                          # 检查所有软限制

ulimit -n 10240                     # 临时生效，重启失效
vi /etc/security/limits.d/xxx.conf  # 如果值太小，则修改该文件，持久生效
*        -    nofile         65535  # redis:64000
*        -    nproc        40960    # redis:64000

说明：修改配置文件只能对新的session起作用。如果要想即时生效，可以通过 ulimit -n 20000 等开启，前提是 新的数值不能超过hard所设定的值。hard值一旦被设定，就不能够再增加。

ulimit 与 systemd 的配置映射表

ulimit setrlimit systemd description
-b The maximum socket buffer size
-c RLIMIT_CORE LimitCORE The maximum size of core files created
-d RLIMIT_DATA LimitDATA The maximum size of a process's data segment
-e RLIMIT_NICE LimitNICE The maximum scheduling priority ("nice")
-f RLIMIT_FSIZE LimitFSIZE The maximum size of files written by the shell and its children
-i RLIMIT_SIGPENDING LimitSIGPENDING The maximum number of pending signals
-l RLIMIT_MEMLOCK LimitMEMLOCK The maximum size that may be locked into memory
-m RLIMIT_RSS LimitRSS The maximum resident set size (many systems do not honor this limit)
-n RLIMIT_NOFILE LimitNOFILE The maximum number of open file descriptors (most systems do not allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be set)
-q RLIMIT_MSGQUEUE LimitMSGQUEUE The maximum number of bytes in POSIX message queues
-r RLIMIT_RTPRIO LimitRTPRIO The maximum real-time scheduling priority
RLIMIT_RTTIME LimitRTTIME
-s RLIMIT_STACK LimitSTACK The maximum stack size
-t RLIMIT_CPU LimitCPU The maximum amount of cpu time in seconds
-u RLIMIT_NPROC LimitNPROC The maximum number of processes available to a single user
-v RLIMIT_AS LimitAS The maximum amount of virtual memory available to the shell and, on some systems, to its children
-x RLIMIT_LOCKS LimitLOCKS The maximum number of file locks
-T The maximum number of threads

systemd 示例

[Unit]
Description=MongoDB Server
After=network.target

[Service]
User=mongod
Group=mongod
Type=forking

PIDFile=/data0/mongod/mongod.pid
ExecStartPre=
ExecStart=/usr/bin/mongod -f /etc/mongod.conf
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s QUIT $MAINPID
WorkingDirectory=/data0/mongod
Restart=always

LimitFSIZE=infinity
LimitCPU=infinity
LimitAS=infinity
LimitNOFILE=64000
LimitRSS=infinity
LimitNPROC=64000

PrivateTmp=true

[Install]
WantedBy=multi-user.target

修改信号量设置

see Setting Semaphore Parameters

# 检查当前值
cat /proc/sys/kernel/sem
250    32000    32    128

# 检查当前值
ipcs -ls

# 查看 cookie
ipcs


# （临时）修改信号量
echo 250 32000 100 128 > /proc/sys/kernel/sem
sysctl -w kernel.sem="250 32000 100 128"

# （持久）修改信号量
echo "kernel.sem=250 32000 100 128" >> /etc/sysctl.conf