Skip to content
This repository has been archived by the owner on Jul 19, 2024. It is now read-only.

rustjson/LearningNote

BranchesTags

Repository files navigation

交个朋友 点这里

#lsof usage Show port listen

#show port 80
lsof -i :80

COMMAND   PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
nginx   14052   root    6u  IPv4 303704      0t0  TCP *:http (LISTEN)
nginx   14053 nobody    6u  IPv4 303704      0t0  TCP *:http (LISTEN)

example of update-alternatives

#add 
sudo update-alternatives --install /usr/bin/phpize phpize /home/jason/php/5.4.11/bin/phpize 1 
#config
sudo update-alternatives --config phpize

#remove
sudo update-alternatives --remove phpize /usr/local/php/5.4.11/bin/php-phpize

source of brk

https://github.com/torvalds/linux/blob/master/mm/mmap.c#L286

Q: Why this won't seg me?

Q：为什么操作(base + 1)不会出现段错误？

#include <stdio.h>
#include <unistd.h>

int main() {
    int *base = sbrk(0);
        
    brk(base + 1);//expand 4bytes(sizeof int) memory 
                                                                        
    printf("base.addr=%p\n", base);
    printf("base+1.addr=%p\n", base + 1); 
    printf("After, brk(), current.addr=%p\n", sbrk(0));
    
    *base = 1; #comment out brk, It will seg here.
    *(base + 1)  = 1;#Why It won't seg me here.

    return 0;
}

A: Because it is page aligned!

A: 因为brk内部也有页对齐！

#include <stdio.h>
#include <unistd.h>

int main() {
    int *base = sbrk(0);
    int pagesize = getpagesize();

    brk(base + 1);//Here are page aligned!!!!!!!!                       

    printf("pagesize=%d\n", pagesize);
    printf("base.addr=%p\n", base);
    printf("base+1.addr=%p\n", base + 1); 
    printf("After, brk(), current.addr=%p\n", sbrk(0));
    
    *base = 1;
    *(base + pagesize/sizeof(int) - 1)   = 1;
    printf("Next, please seg me!\n");
    *(base + pagesize/sizeof(int))   = 1;
    //sleep(10000); sleep a long time, I need to get
    //the virtual address range of the heap of this program
    //sudo cat /proc/PID/maps |grep heap
    return 0;
}

A:Another proof:

A：另外一个证明的方法：

sudo cat /proc/PID/maps |grep heap
#This command could get the virtual address of heap, result are the same
#with output of above progrma 
#通过这个命令拿到堆的地址，和上面程序打印出来的地址完全一模一样

How to get source code of basic command in ubuntu like ls top etc

在ubuntu下如何找到基本命令(ls top等)的源码

> dpkg -S /bin/ls
coreutils: /bin/ls
#So coreutils is the package that contains command ls.

Then goto this page Ubuntu – Ubuntu Packages Search, search it by using that keyword

然后到这个页面Ubuntu – Ubuntu Packages Search里用得到的关键字搜索

top's package download page： http://packages.ubuntu.com/trusty/procps ，On the right side!

top所在包的下载页面 http://packages.ubuntu.com/trusty/procps 右边有一个souce下载。是他是他就是他！

What if the difference of Shared and Clean?

Shared_Clean:          0 kB
Shared_Dirty:          0 kB
Private_Clean:         0 kB
Private_Dirty:         0 kB
Referenced:            0 kB
Anonymous:             0 kB
AnonHugePages:         0 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:                0 kB

Both Shared and Clean has two part of Clean and Dirty. But what does that respent? see stackexchange

Dirty 表示页是脏的, 即与磁盘后备文件的内容不一致, 需要(或正在)写回后备设备 Clean 表示页的内容和后备是一致的.

See fs/proc/task_mmu.c#show_smap See /mm/pagewalk.c#walk_page_range

For both difference of private and shared, dirty and clean : See private_dirty_modify

When talking about private and shared, that is simple, as code shows,

if (page_mapcount(page)>=2) {
    //shared
} else {
    //private
}

ref: How much memory are applications really using? pagemap - The Linux Kernel Archives

fcntl(fd, F_SETFD, FD_CLOEXEC)

It sets the close-on-exec flag for the file descriptor, which causes the file descriptor to be automatically (and atomically) closed when any of the exec-family functions succeed.stackoverflow

What happend to fd when a parent process exit without waitpid() his child.

#include <stdio.h>
#include <unistd.h>

int main() {
    int pid = -1; 
    char buf[10] = {0};

    pid = fork();
    if (pid == -1) {
        perror("fork");
    }   
    if (pid == 0) {//child
        printf("[child]sleeping\n");
        sleep(2);//sleep to wait parent exit;
        write(1, "[child]nihao\n", 13);
        if (read(0, buf, 1) == -1) {
            printf("[child]ops, read error\n");
        }   
        _exit(0);
    } else {
        printf("[parent]exit\n");
        //if (waitpid(pid, NULL, 0) < 0) {
        //     perror("waitpid error\n");
        //} 
        _exit(0);   
    }   
}
sunan at Sunan-ubuntu in ~/c/more
○ ./fd-on-close 
[parent]exit
[child]sleeping

sunan at Sunan-ubuntu in ~/c/more
○ [child]nihao
[child]ops, read error

See ? You can still write, but can't read.

Why async curl slower then curl on a 8 core machine when curl a static page servie by nginx

This graph show, async request has no big benefit compare with normal request So, I take a took of libcurl and run another example: https://raw.githubusercontent.com/bagder/curl/master/docs/examples/multi-app.c This guy was the author of libcurl :[https://github.com/bagder/]

curl/curl#519

I think htop won't see the thread was it create and destory too fast. since debug could see every thread by it.

By the way, HTOP are a really good program!

Something relate gcc and linker and library

See this Makefile

CC=gcc

all : multi-app httpcustomheader 10-at-a-time

multi-app: multi-app.c
	${CC} -g multi-app.c -lcurl -o multi-app

httpcustomheader: httpcustomheader.c
	${CC} -g httpcustomheader.c -lcurl -o httpcustomheader
10-at-a-time: 10-at-a-time.c
	${CC} -g 10-at-a-time.c -L/usr/local/curl/lib -I/usr/local/include -lcurl -o 10-at-a-time

Note that -I means include path. -L means library path. -l seems indicates we need that library! Also, We can use this LD_PRELOAD=/usr/local/curl/lib/libcurl.so strace -eclone ./multi-app to force our multi-app use libcurl.so as it's library. You can use LD_PRELOAD=/usr/local/curl/lib/libcurl.so strace -eopen ./multi-app to comfirm that. export LD_LIBRARY_PATH=/usr/local/curl/lib seems another good choose, But be aware of this:

open("/etc/ld.so.preload", O_RDONLY|O_CLOEXEC) = 3
open("/lib/lib/x86_64-linux-gnu/liblsp.so", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/tls/x86_64/libcurl.so.4", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/local/curl/lib/tls/libcurl.so.4", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/local/curl/lib/x86_64/libcurl.so.4", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/local/curl/lib/libcurl.so.4", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/libidn.so.11", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/libidn.so.11", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/librtmp.so.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/librtmp.so.0", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/libssl.so.1.0.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libssl.so.1.0.0", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/libcrypto.so.1.0.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libcrypto.so.1.0.0", O_RDONLY|O_CLOEXEC) = 3
open("/usr/local/curl/lib/liblber-2.4.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

It will load all the shared library from this path. So, I don't think this is a good ieda.
See here

Why execute a new command by using ./a.out always create a new process group ?

为什么./执行出来的命令总是一个新的进程组？

Guess:

猜：

Inside ./a.out, bash create execute clone() and then setpgid(0, PID) then execve(a.out...)

当你执行./a.out的时候，系统一次执行clone()然后，setpgid(0, PID) 然后 execve(a.out...)

Prof:

证明：

//newgroup.c
#include <stdlib.h>
#include <stdio.h>

int main() {
	printf("This is a marker\n");
	sleep(1000);
	return 0;
}

Let's compile this file to newgroup and then use strace to trace our zsh,

In my test, the PID of zsh is 9421, so simply open a new terminal and execute this:

sudo strace -esetpgid,execve,write,clone -p 9421 -f -v

And then execute our newgroup:

./newgroup

Outputs looks like this:

Process 9421 attached



write(1, "\33[?1l\33>", 7)              = 7
write(10, "\r\n", 2)                    = 2
write(3, ": 1446459559:0;./newgroup \n", 27) = 27
write(1, "\33]2;./newgroup\7", 15)      = 15
write(1, "\33]1;./newgroup\7", 15)      = 15
clone(Process 17943 attached
child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f4de73aba10) = 17943
[pid 17943] setpgid(0, 17943)           = 0
[pid 17943] execve("./newgroup", ["./newgroup"], ["SESSION_MANAGER=local/Sunan-ubun"..., "XDG_SESSION_ID=c2", "LC_IDENTIFICATION=en_US.UTF-8", "XDG_SEAT=seat0", "DISPLAY=:0", "JOB=dbus", "COLORTERM=gnome-terminal", "GNOME_KEYRING_CONTROL=/run/user/"..., "GNOME_DESKTOP_SESSION_ID=this-is"..., "DEFAULTS_PATH=/usr/share/gconf/u"..., "QT_QPA_PLATFORMTHEME=appmenu-qt5", "LOGNAME=sunan", "TEXTDOMAIN=im-config", "INSTANCE=", "LC_TIME=en_US.UTF-8", "SHELL=/bin/zsh", "PATH=/home/sunan/google-cloud-sd"..., "LC_NUMERIC=en_US.UTF-8", "LC_PAPER=en_US.UTF-8", "IM_CONFIG_PHASE=1", "TEXTDOMAINDIR=/usr/share/locale/", "CLUTTER_IM_MODULE=xim", "QT4_IM_MODULE=fcitx", "XDG_SESSION_PATH=/org/freedeskto"..., "SESSION=ubuntu", "SSH_AUTH_SOCK=/run/user/1000/key"..., "XDG_MENU_PREFIX=gnome-", "XAUTHORITY=/home/sunan/.Xauthori"..., "QT_IM_MODULE=xim", "GDMSESSION=ubuntu", "XMODIFIERS=@im=fcitx", "LC_MEASUREMENT=en_US.UTF-8", "LC_ADDRESS=en_US.UTF-8", "XDG_CONFIG_DIRS=/etc/xdg/xdg-ubu"..., "MANDATORY_PATH=/usr/share/gconf/"..., "UPSTART_SESSION=unix:abstract=/c"..., "XDG_RUNTIME_DIR=/run/user/1000", "DESKTOP_SESSION=ubuntu", "GTK_IM_MODULE=fcitx", "GTK_MODULES=overlay-scrollbar:un"..., "USER=sunan", "PWD=/home/sunan/c/more", "VTE_VERSION=3409", "LC_MONETARY=en_US.UTF-8", "HOME=/home/sunan", "XDG_SEAT_PATH=/org/freedesktop/D"..., "XDG_DATA_DIRS=/usr/share/ubuntu:"..., "LANGUAGE=fr_FR:en", "SELINUX_INIT=YES", "COMPIZ_CONFIG_PROFILE=ubuntu", "XDG_GREETER_DATA_DIR=/var/lib/li"..., "COMPIZ_BIN_PATH=/usr/bin/", "LC_NAME=en_US.UTF-8", "LANG=en_US.UTF-8", "GPG_AGENT_INFO=/run/user/1000/ke"..., "SHLVL=1", "WINDOWID=75497483", "XDG_VTNR=7", "GDM_LANG=fr_FR", "SESSIONTYPE=gnome-session", "DBUS_SESSION_BUS_ADDRESS=unix:ab"..., "XDG_CURRENT_DESKTOP=Unity", "TERM=xterm", "GNOME_KEYRING_PID=2567", "LC_TELEPHONE=en_US.UTF-8", "OLDPWD=/home/sunan/c", "ZSH=/home/sunan/.oh-my-zsh", "GOPATH=/home/sunan/golang", "GOROOT=/home/sunan/go/src/go1.5", "PAGER=less", "LESS=-R", "LC_CTYPE=fr_FR.UTF-8", "LSCOLORS=Gxfxcxdxbxegedabagacad", "_=/home/sunan/c/more/./newgroup"]) = 0
[pid 17943] write(1, "This is a marker\n", 17) = 17

How to free cached mem in Linux

How to change file permission under git with core.filemode=false

http://stackoverflow.com/questions/10516201/updating-file-permissions-only-in-git

好吧别理我，我今天早上没吃:pill:

About

My Learning Notes:sheep:

Resources

Readme
Activity

Stars

4 stars

Watchers

2 watching

Forks

1 fork
Report repository

Releases

No releases published

Packages

No packages published

Languages