signal SIGSEGV: address not mapped to object (fault address: 0x20)

static function不需要被呼叫就有可能發生錯誤

dlopen無法載入函示庫

https://stackoverflow.com/a/2991677/22299707

1. 用ldd -r 列出所以找不到的函式庫像這樣

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   linux-vdso.so.1 (0x00007ffcfd376000) libjson-glib-1.0.so.0 => /lib/x86_64-linux-gnu/libjson-glib-1.0.so.0 (0x00007f210d72c000) ..... undefined symbol: descriptor_table_google_2fprotobuf_2ftimestamp_2eproto (./libnvds_msgconv.so) undefined symbol: _ZN6google8protobuf7Message17CopyWithSizeCheckEPS1_RKS1_ (./libnvds_msgconv.so) .....

2. 用c++filt顯示函式庫名稱，還原函數名稱

   1	c++filt _ZN6google8protobuf7Message17CopyWithSizeCheckEPS1_RKS1_

參考

https://cynthiachuang.github.io/Enforce-Password-Policies-and-Force-User-to-Change-Password-in-Linux/

1. 注意題目裡的線索
   例如題目如果出現”寫一個在伺服器長時間重複運作的程式”，你可以想看看快取是不是可以派上用場

2. 寫出測試範例
   要特別注意自己寫出來的範例是不是特例

3. 嘗試暴力解

4. 優化

Check Permutation: Given two strings, write a method to decide if one is a permutation of the other. p.90

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def check_permutation(s1, s2):
    if len(s1) != len(s2):
        return False
    sd1 = {}
    for i in s1:
        if sd1.get(i):
            sd1[i] = sd1[i] + 1
        else:
            sd1[i] = 1
    for j in s2:
        if sd1.get(j):
            if sd1.get(j) > 0:
                sd1[i] = sd1[i] - 1
            else:
                return False
        else:
            return False
    return True
        

samples

• dad, bda
• abc, bca
• sss, sss
• sas, ssa
• abcd, abc
• bbba, bbbb

URLify: Write a method to replace all spaces in a string with ‘%20’. You may assume that the string has sufficient space at the end to hold the additional characters, and that you are given the “true” length of the string. (Note: If implementing in Java, please use a character array so that you can perform this operation in place.)

• 錯誤1:
  忘記回傳值

Palindrome Permutation: Given a string, write a function to check if it is a permutation of a palin-drome. A palindrome is a word or phrase that is the same forwards and backwards. A permutation is a rearrangement of letters. The palindrome does not need to be limited to just dictionary words.

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import copy

def palindrome(input):
    input = input.lower()
    char_dict = {}
    for c in input:
        if c != " ":
            if char_dict.get(c):
                char_dict.pop(c)
            else:
                char_dict[c] = 1
    if len(char_dict) > 1:
        return False
    return True

錯誤1: 沒有考慮到大小寫問題

One Away: There are three types of edits that can be performed on strings: insert a character, remove a character, or replace a character. Given two strings, write a function to check if they are one edit (or zero edits) away.

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def one_edit(str_a, str_b):
    if len(str_a) - len(str_b) == -1:
        for c in str_a:
            if c not in str_b:
                return False
    elif len(str_a) - len(str_b) == 1:
        for c in str_b:
            if c not in str_a:
                return False
    elif len(str_a) - len(str_b) == 0:
        counter = 0
        for c in str_a:
            if c not in str_b:
                counter +=1
        if counter > 1:
            return False
    else:
        return False
    return True

移除服務

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systemctl disable [servicename]
sudo trash /etc/systemd/system/[servicename]
sudo trash /etc/systemd/system/[servicename] # and symlinks that might be related
sudo trash /usr/lib/systemd/system/[servicename] 
sudo trash /usr/lib/systemd/system/[servicename] # and symlinks that might be related
systemctl daemon-reload
systemctl reset-failedbash

https://superuser.com/a/936976

Failed to detect a default CUDA architecture或是CMAKE_CUDA_ARCHITECTURES must be non-empty if set

直接告訴CMake nvcc的位置，注意舊的build資料夾要先清掉
-DCMAKE_CUDA_COMPILER=/usr/local/cuda-11.7/bin/nvcc

https://www.cnblogs.com/metaz/p/16919028.html

VS code設定cmake的環境變數

在setting.json加入"cmake.environment": {"CUDA_VER":"11.7"}，說明書:https://github.com/microsoft/vscode-cmake-tools/blob/main/docs/cmake-presets.md#ignored-settings

CMake presets: https://dominikberner.ch/cmake-presets-best-practices/

CMake 系統環境變數設置

https://www.scivision.dev/cmake-environment-variable-scope/

libcuda.so.1 not found

使用find_package(CUDAToolkit)並且在target_link_libraries 加入CUDA::cuda_driver

CMake find_package() 用法

CMake有許多尋找套件的module，例如FindCUDAToolkit，下面連結條列各種find_package()能使用的module

https://cmake.org/cmake/help/latest/manual/cmake-modules.7.html#manual:cmake-modules(7)

服務無法啟動，Kafka Broker doesn’t find cluster id

移除meta.properties.

參考:https://stackoverflow.com/questions/59592518/kafka-broker-doesnt-find-cluster-id-and-creates-new-one-after-docker-restart

資源監視器btop

https://github.com/aristocratos/bpytop#installation

apt找不到key或重複套件，刪掉有問題的apt key

sudo rm /etc/apt/sources.list.d/*cuda*

查看所有可以安裝的版本

apt-cache madison cuda

https://askubuntu.com/questions/447/how-can-i-see-all-versions-of-a-package-that-are-available-in-the-archive

刪除apt key

• 顯示所有key
  apt-key list顯示結果如下

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  /etc/apt/trusted.gpg -------------------- pub rsa4096 2022-05-05 [SCEA] 8298 D919 610D E70B 90CE DAAE EE38 2EF7 8230 7095 uid [ unknown] TensorRT <svc_tensorrt@nvidia.com> /etc/apt/trusted.gpg.d/flexiondotorg_ubuntu_nvtop.gpg ----------------------------------------------------- pub rsa1024 2011-03-16 [SC] 824A 27DD 09DE DA33 BF78 3596 2EA8 F357 93D8 809A uid [ unknown] Launchpad PPA for Martin Wimpress /etc/apt/trusted.gpg.d/graphics-drivers_ubuntu_ppa.gpg ------------------------------------------------------ pub rsa4096 2015-08-12 [SC] 2388 FF3B E10A 76F6 38F8 0723 FCAE 110B 1118 213C uid [ unknown] Launchpad PPA for Graphics Drivers Team

• 刪掉key
  以下面為例，key ID就是最後8碼82307095，sudo apt-key del 82307095就可以刪除

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/etc/apt/trusted.gpg
--------------------
pub   rsa4096 2022-05-05 [SCEA]
      8298 D919 610D E70B 90CE  DAAE EE38 2EF7 8230 7095
uid           [ unknown] TensorRT <svc_tensorrt@nvidia.com>

解決Unmet dependencies問題

• 用dpkg -P package-name來移除有問題的套件，他會顯示不能移除的原因，然後依序移除即可

• 直接用dpkg安裝套件，如果有缺少的相依套件，之後使用apt install就會顯示E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).錯誤，必須要手動解決相依性問提

apt install使用local repo

參考: https://wiki.debian.org/DebianRepository/Setup?action=show&redirect=DebianRepository%2FHowTo%2FTrivialRepository#trivialArchive

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Quick instructions to create a trivial local archive with apt-ftparchive
We use /var/lib/mydebs as the example location

Create the directory

  mkdir -p /var/lib/mydebs
Every time you put new files in the directory, you'll have to scan the directory and update:

  cd /var/lib/mydebs
  apt-ftparchive packages . > Packages
  apt-ftparchive release . > Release
Add this line to /etc/apt/sources.list

  deb [allow-insecure=yes] file:/var/lib/mydebs ./
Now you can install the package normally. If apt-get asks "Install these packages without verification?", answer "Y" to install. That's because this local repository is not signed.

  apt-get update
  apt-get install mydeb

刪除apt gpg key 和repo

https://itslinuxfoss.com/delete-repository-and-gpg-key-ubuntu/#2

查看套件版本

dpkg-query -W tensorrt

用apt 查看可安裝的版本

apt-cache policy <package name>

例如

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$ apt-cache policy gparted
gparted:
  Installed: 0.16.1-1
  Candidate: 0.16.1-1
  Version table:
 *** 0.16.1-1 0
        500 http://ubuntu.inode.at/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status

安裝指定版本
sudo apt-get install <package name>=<version>
例如上面的例子

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$ sudo apt-get install gparted=0.16.1-1
Reading package lists... Done
Building dependency tree       
Reading state information... Done
gparted is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 265 not upgraded.

BigO

• 時間複雜度相加還是相乘
  相加

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  Add the Runtimes: 0 (A + B) 1 for (int a : arrA) { 2 print(a); 3 } 4 5 for (int b : arrB) { 6 print(b) ; 7 }

相乘:

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Multiply the Runtimes: O(A* B) 
1  for  (int  a  :  arrA)  { 
2      for  (int  b  :  arrB)  { 
3          print(a  +  " , "  +  b); 
4      }     
5  } 

• 遞迴的時間複雜度