Open-Wrt: Add hello world application

In this section, you are going to learn

How to create a simple application in Open-WRT ?

How to generate full openwrt image for RPI-4B ?

How to flash full openwrt image for RPI-4B ?

How to run minicom and work remotely with RPI-4B ?

Topics in this section,

• Step 0: How to clone and build base openWRT image ?

• Step 1: Add custom application

  • Step 1.1: Add directory structure of application package

  • Step 1.2: Create directory under package directory

  • Step 1.3: Create helloworld.c

  • Step 1.4: Create Makefile

  • Step 1.5: Explanation of Makefile part by part

• Step 2 : Add application package to menuconfig

  • Step 2.1: Create feeds.conf file

  • Step 2.2: Content of feeds.conf

  • Step 2.3: Below example for feeds path

• Step 3 : Update and install feeds

  • Step 3.1: Commands for update and install feeds

• Step 4 : Enable application package in menuconfig

  • Step 4.1: Select your application in menuconfig

  • Step 4.2: Save the configuration

  • Step 4.3: Exit the menuconfig

• Step 5: Do Pre-Build checks

  • Step 5.1: Check .config file is present or not

  • Step 5.2: Check the location of toolchain

• Step 6: Build application package

• Step 7: Do post build checks

  • Step 7.1 Check the location of the application binary file

  • Step 7.2 : Check the “objdump” output of the application binary file

  • Step 7.3 : Check the “readelf” output of the application binary file

  • Step 7.4 : Check the “nm” output of the application binary file

  • Step 7.5 : Check the “file” command output of application binary file

  • Step 7.6 : Check the “size” command output of application binary file

  • Step 7.7 : Check the “strings” command output of application binary file

  • Step 7.8: Check the location of .ipk file

  • Step 7.9: How to extract .ipk file

  • Step 7.10: How to check content of .ipk file

• Step 8: Build full openwrt - Incremental

  • Step 8.1: Do Pre-Build checks

  • Step 8.2: Build full openwrt

  • Step 8.3: Do Post-Build checks

Step 0: How to clone and build base openWRT image ?

• Step 1: Clone

  $ cd $HOME
  
  $ git clone https://github.com/openwrt/openwrt.git
  
  $ cd openwrt
  

• Step 2: Update and install latest feeds

  $ ./scripts/feeds update -a
  
  $ ./scripts/feeds install -a
  

• Step 3: Do make menuconfig

  $ make menuconfig
  

• Step 4: Save the configuration

• Step 5: Exit the menuconfig

• Step 6: Check .config file

  Step 6.1: In menuconfig select Network and sub Network of WirelessAPD there will enable

  • Make sure the current directory “openwrt”

  • In .config file package should be enabled in ‘y’

  • Check those lines in .config file

  CONFIG_PACKAGE_hostapd=y
  CONFIG_PACKAGE_hostapd-basic=m
  CONFIG_PACKAGE_hostapd-basic-openssl=m
  CONFIG_PACKAGE_hostapd-basic-wolfssl=m
  CONFIG_PACKAGE_wpa-cli=y
  CONFIG_PACKAGE_wpa-supplicant=y
  CONFIG_PACKAGE_wpa-supplicant-basic=m
  CONFIG_PACKAGE_wpa-supplicant-mini=m
  CONFIG_PACKAGE_wpa-supplicant-openssl=m
  CONFIG_PACKAGE_wpa-supplicant-p2p=m
  CONFIG_PACKAGE_wpa-supplicant-wolfssl=m
  CONFIG_PACKAGE_wpad-basic-wolfssl=m
  

  Step 6.2: In menuconfig select Network

  • Make sure the current directory “openwrt”

  • In .config file package should be enabled in ‘y’

  • Check those lines in .config file

  CONFIG_PACKAGE_ethtool=y
  CONFIG_PACKAGE_fping=y
  CONFIG_PACKAGE_iperf=y
  CONFIG_IPERF_ENABLE_MULTICAST=y
  CONFIG_PACKAGE_iperf3=y
  CONFIG_PACKAGE_iputils-arping=y
  CONFIG_PACKAGE_iputils-ping=y
  CONFIG_PACKAGE_tcpdump=y
  

  Step 6.3: In menuconfig select Base System

  • Make sure the current directory “openwrt”

  • In .config file package should be enabled in ‘y’

  • Check those lines in .config file

  CONFIG_PACKAGE_procd-ujail=y
  CONFIG_PACKAGE_swconfig=y
  CONFIG_PACKAGE_uci=y
  CONFIG_PACKAGE_urandom-seed=y
  CONFIG_PACKAGE_urngd=y
  CONFIG_PACKAGE_wireless-tools=y
  

• Step 7: Build

  $ make
   make[1] world
   make[2] target/compile
   make[3] -C target/linux compile
   make[2] buildinfo
   make[3] diffconfig buildversion feedsversion
   make[2] package/cleanup
   make[2] package/compile
   .
   .
   make[2] target/install
   make[3] -C target/linux install
   make[2] package/index
   make[2] json_overview_image_info
   make[2] checksum
  

• Step 8: Check the location of the image

  $ pwd
  
    /home/test/openwrt
  

  $HOME/openwrt/bin/targets/bcm27xx/bcm2711/
  
  $ ls -l
  
    -rw-r--r-- 1 sysadmin sysadmin     1527 Dec 29 19:45 config.buildinfo
    -rw-r--r-- 1 sysadmin sysadmin     83 Dec 29 19:45 feeds.buildinfo
    -rw-r--r-- 1 sysadmin sysadmin     17075452 Dec 29 19:47 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
    -rw-r--r-- 1 sysadmin sysadmin     17076299 Dec 29 19:47 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
    -rw-r--r-- 1 sysadmin sysadmin     4126 Dec 29 19:47 openwrt-bcm27xx-bcm2711-rpi-4.manifest
    -rw-r--r-- 1 sysadmin sysadmin     15316637 Dec 29 19:47 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
    -rw-r--r-- 1 sysadmin sysadmin     15317484 Dec 29 19:47 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
    drwxr-xr-x 2 sysadmin sysadmin     4096 Dec 29 19:47 packages
    -rw-r--r-- 1 sysadmin sysadmin     2141 Dec 29 19:47 profiles.json
    -rw-r--r-- 1 sysadmin sysadmin     912 Dec 29 19:47 sha256sums
    -rw-r--r-- 1 sysadmin sysadmin     18 Dec 29 19:45 version.buildinfo
  

Step 1 : Add custom application

In this section you will learn how to add custom application

Step 1.1: Add directory structure of application package

• Make sure the current directory “openwrt”

  $ pwd
  
    /home/test/openwrt
  

Step 1.2: Create directory under package directory

• Make sure the current directory “openwrt”

  $ cd package
  
  $ mkdir -p mypackages/examples/helloworld
  
  $ cd mypackages/examples/helloworld/helloworld
  

Step 1.3: Create helloworld.c

• Create helloworld.c file using vim command

  vim helloworld.c
  

• Content of helloworld.c

  #include <stdio.h>
  
  void app_fun(void)
  {
          printf("Hi, application\n");
  }
  
  int main(void)
  {
          printf("Hello, world!\n");
          app_fun();
  
          return 0;
   }
  

Step 1.4: Create Makefile

• Create Makefile file using vim command

  vim Makefile
  

• Content of Makefile

  include $(TOPDIR)/rules.mk
  
  PKG_NAME:=helloworld
  PKG_VERSION:=1.0
  PKG_RELEASE:=1
  
  SOURCE_DIR:=$(TOPDIR)/package/mypackages/examples/helloworld
  
  include $(INCLUDE_DIR)/package.mk
  
  define Package/helloworld
  SECTION:=examples
  CATEGORY:=Examples
  TITLE:=Hello, World!
  endef
  
  define Package/helloworld/description
  A simple "Hello, world!" -application.
  endef
  
  define Build/Prepare
          mkdir -p $(PKG_BUILD_DIR)
          cp $(SOURCE_DIR)/helloworld.c $(PKG_BUILD_DIR)
          cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
          $(Build/Patch)
  endef
  
  define Build/Compile
          $(TARGET_CC) $(TARGET_CFLAGS) -o $(PKG_BUILD_DIR)/helloworld.o -c $(PKG_BUILD_DIR)/helloworld.c
          $(TARGET_CC) $(TARGET_LDFLAGS) -o $(PKG_BUILD_DIR)/$1 $(PKG_BUILD_DIR)/helloworld.o
  endef
  
  define Package/helloworld/install
          $(INSTALL_DIR) $(1)/usr/bin
          $(INSTALL_BIN) $(PKG_BUILD_DIR)/helloworld $(1)/usr/bin
  endef
  
  $(eval $(call BuildPackage,helloworld))
  

Step 1.5: Explanation of Makefile part by part

include $(TOPDIR)/rules.mk

• Explanation of include $(TOPDIR)/rules.mk

  include $(TOPDIR)/rules.mk
  

• The $(TOPDIR) is expected to be the top-level directory of the project

• /rules.mk - The path to the file to be included

What is $(TOPDIR) ?

See Answer

• $(TOPDIR) path is /home/test/openwrt

Package Name, Version and Release number Block

• Explanation of Package Name, Version and Release number Block

PKG_NAME:=helloworld
PKG_VERSION:=1.0
PKG_RELEASE:=1

• The name and version of your package are used to define the variable to point to the build directory of your package (Ex: helloworld-1.0)

Path (absolute or relative) to a directory Block

• Explanation of SOURCE_DIR

SOURCE_DIR:=$(TOPDIR)/package/mypackages/examples/helloworld

What is SOURCE_DIR ?

See Answer

• SOURCE_DIR is relative or absolute path of directory

• In this case path of SOURCE_DIR $HOME/openwrt/package/mypackages/examples/helloworld

• Give path of the source directory

• SOURCE_DIR is used in Build/Prepare

include $(INCLUDE_DIR)/package.mk

• Explanation of include $(INCLUDE_DIR)/package.mk

include $(INCLUDE_DIR)/package.mk

• $(INCLUDE_DIR) - Directory containing include files

• /package.mk: The path to the file to be included

What is $(INCLUDE_DIR) ?

See Answer

• $(INCLUDE_DIR) - It will search for included files

• In this case path of $(INCLUDE_DIR) $HOME/openwrt/include

Package Information Block

• Explanation of Package Information

define Package/helloworld
SECTION:=examples
CATEGORY:=Examples
TITLE:=Hello, World!
endef

• This block defines the package information as section, category, and title

• SECTION: examples: This line tells the section to which the package belongs. In this case, the package will come under the “examples” section.

• CATEGORY: Examples: This line tells the category to which the package belongs. In this case, the category is set to “Examples

• TITLE: Hello, world This line tells, title or name of the package. In this case, the title is set to “Hello, world!”.

• endef: This line will be the end of the define block.

What all information included in Package Information Block ?

See Answer

• It includes section, category, and title

Package Description Block

• Explanation of Package Description

define Package/helloworld/description
A simple "Hello, world!" -application.
endef

• This function defines of package.

What is Package Description Block ?

See Answer

• Instructs on how and where our package will appear in the overall configuration menu

Build/Prepare Block

• Explanation of Build/Prepare

define Build/Prepare
        mkdir -p $(PKG_BUILD_DIR)
        cp $(SOURCE_DIR)/helloworld.c $(PKG_BUILD_DIR)
        cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
        $(Build/Patch)
endef

• mkdir -p $(PKG_BUILD_DIR): This line creates the build directory

• cp $(SOURCE_DIR)/helloworld.c $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• $(Build/Patch): This line includes a call to $(Build/Patch), which is a variable or macro typically defined elsewhere in the Makefile. It is used to apply any necessary patches to the source code.

What is -r ?

See Answer

• -r is recursive copy.

Which path $(PKG_BUILD_DIR) ?

See Answer

• In this case path of $(PKG_BUILD_DIR) $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/helloworld-1.0

What is SOURCE_DIR ?

See Answer

• In this case path of SOURCE_DIR $HOME/openwrt/package/mypackages/examples/helloworld

Build/Compile Block

• Explanation of Build/Compile

define Build/Compile
        $(TARGET_CC) $(TARGET_CFLAGS) -o $(PKG_BUILD_DIR)/helloworld.o -c $(PKG_BUILD_DIR)/helloworld.c
        $(TARGET_CC) $(TARGET_LDFLAGS) -o $(PKG_BUILD_DIR)/$1 $(PKG_BUILD_DIR)/helloworld.o
endef

• This block defines the compilation process.

• $(TARGET_CC): It is said to arm cross compiler and it is defined globally

• $(TARGET_CFLAGS): It is used for additional flags

• -o $(PKG_BUILD_DIR)/helloworld.o: Takes .c input file and generates .o output file in location $(PKG_BUILD_DIR)

• -o $(PKG_BUILD_DIR)/$1: The final helloworld binary will be placed in the build directory ($(PKG_BUILD_DIR)).

What is $(TARGET_CC) ?

See Answer

• It is said to arm cross compiler

• In this case path of $(TARGET_CC) $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/bin

What is $(TARGET_CFLAGS) ?

See Answer

• It is used for additional flags

Package Install Block

• Explanation of Package Install

define Package/helloworld/install
        $(INSTALL_DIR) $(1)/usr/bin
        $(INSTALL_BIN) $(PKG_BUILD_DIR)/helloworld $(1)/usr/bin
endef

• $(INSTALL_DIR): It used for creating a directory and it is commonly used in build systems like OpenWrt.

• $(INSTALL_BIN): It used for copying an executable file.

• /usr/bin: It is the destination directory, binary file will be installed.

What is $(INSTALL_DIR) ?

See Answer

• It used for creating a directory

• In this case $(INSTALL_DIR) install -d -m0755

• Install command is used to copy files and set attributes.

• -d, –directory : It will act as directory names towards all arguments.

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(INSTALL_BIN) ?

See Answer

• It used for copying an executable file.

• In this case $(INSTALL_BIN) install -m0755

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(1)/usr/bin ?

See Answer

• /usr/bin: It is the destination directory where the binary executable will be installed.

• In this case path of $(1)/usr/bin $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/helloworld-1.0/.pkgdir/helloworld/usr/bin

Package Build Block

• Explanation of Package Build

$(eval $(call BuildPackage,helloworld))

• BuildPackage: It is function call with helloworld as parameter.

Step 2 : Add application package to menuconfig

In this section you will learn how to add menuconfig

Step 2.1: Create feeds.conf file

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

$ vim feeds.conf

Step 2.2: Content of feeds.conf

• Inside feeds.conf

src-link <name> <path>

Step 2.3: Below example for feeds path

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

src-link mypackages /home/test/openwrt/package/mypackages

Step 3 : Update and install feeds

In this section you will learn how to install and update feeds

Step 3.1: Commands for update and install feeds

• Installs the most recent packages, replacing any earlier versions that were already on your system

$ ./scripts/feeds update -a

$ ./scripts/feeds install -a -f

Step 4 : Enable application package in menuconfig

In this section you will learn how to enable in menuconfig

Step 4.1: Select your application in menuconfig

• Select your category that reflects in menuconfig

• Go inside examples and select helloworld

Step 4.2: Save the configuration

Step 4.3: Exit the menuconfig

Step 5: Do Pre-Build checks

In this section you will learn how to do Pre-build checks

Step 5.1: Check .config file is present or not

• In .config file package should be enabled in ‘y’

• Below line should be present in .config file

  CONFIG_PACKAGE_helloworld=y
  

Step 5.2 : Check the location of toolchain

• Make sure the current directory “openwrt”

  $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl
  

  $ ls -l
  
   drwxr-xr-x 2 sysadmin sysadmin 4096 Dec 23 02:58 bin
   drwxr-xr-x 3 sysadmin sysadmin 4096 Dec 23 03:39 include
   lrwxrwxrwx 1 sysadmin sysadmin    6 Dec 23 03:39 lib -> ../lib
   lrwxrwxrwx 1 sysadmin sysadmin    8 Dec 23 03:20 lib64 -> ../lib64
   lrwxrwxrwx 1 sysadmin sysadmin   10 Dec 23 03:39 sys-include -> ../include
  

Step 6: Build application package

• Make sure the current directory is ‘helloworld-1.0’

  $HOME/openwrt
  
  $ make package/helloworld/compile
  

Step 7: Do post build checks

In this section you will learn about post build checks

Step 7.1 Check the location of the application binary file

• Make sure the current directory is ‘helloworld-1.0’

$ pwd

  /home/test/openwrt

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/helloworld-1.0

$ ls -l

  -rwxr-xr-x 1 sysadmin sysadmin        72880 Dec 29 19:46 helloworld
  -rw-r--r-- 1 sysadmin sysadmin        146 Dec 29 19:46 helloworld.c
  -rw-r--r-- 1 sysadmin sysadmin        1992 Dec 29 19:46 helloworld.o
   drwxr-xr-x 3 sysadmin sysadmin       4096 Dec 29 19:46 ipkg-aarch64_cortex-a72
  -rw-r--r-- 1 sysadmin sysadmin        1430 Dec 29 19:46 Makefile

See that binary called helloworld is present inside directory ?

See Answer

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/helloworld-1.0

$ ls -l

• -rwxr-xr-x 1 sysadmin sysadmin 72880 Dec 29 19:46 helloworld

Step 7.2: Check the “objdump” output of the application binary file

Step 7.2.1: Check “objdump” -t

• Let check objdump” output of the application binary file

• objdump -t : Displays the symbols of application binary file

• Check if “main” is present or not in the “objdump”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump -t helloworld | grep -i main

00000000004004f0 g     F .text     0000000000000024              main

What is “-t” option is used in “objdump” command ?

See Answer

• -t: Displays the symbols of application binary file

What “objdump” command does ?

See Answer

• objdump: Display information from object files

• Check if “app_fun” is present or not in the “objdump”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump -t helloworld | grep -i app_fun

00000000004005c0 g     F .text   000000000000000c              app_fun

• Symbols “main” and “app_fun” are present in application binary file

• Hence we can confirm application is compiled successfully

Step 7.2.2: Check “objdump” -S

• objdump -S : Display source code intermixed with disassembly

• Check if “main” is present or not in the “objdump”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump -S helloworld | grep -i main

00000000004004f0 <main>:

What is “-S” option is used in “objdump” command ?

See Answer

• -S : Display source code intermixed with disassembly

What is the purpose of “objdump” command ?

See Answer

• The main purpose of the objdump tool is to debug and understand the executable file

• Check if “app_fun” is present or not in the “objdump”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump -S helloworld | grep -i app_fun

400504: 9400002f        bl      4005c0 <app_fun>
00000000004005c0 <app_fun>:

• Symbols “main” and “app_fun” are present in application binary file

• Hence we can confirm application is compiled successfully

Step 7.3: Check the “readelf” output of the application binary file

Step 7.3.1: Check “readelf” -s

• readelf -s: Display the symbol table

• Check if “main” is present or not in the “readelf”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/readelf -s helloworld | grep -i main

79: 00000000004004f0    36 FUNC    GLOBAL DEFAULT   12 main

What is “-s” option is used in “readelf” command ?

See Answer

• -s: Display the symbol table

What “readelf” command does ?

See Answer

• readelf: Display information about ELF files

What is the purpose of “readelf” command ?

See Answer

• The main purpose of the readelf tool is to display the headers of an ELF (Executable and Linkable Format) files

• Check if “app_fun” is present or not in the “readelf”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/readelf -s helloworld | grep -i app_fun

81: 00000000004005c0    12 FUNC    GLOBAL DEFAULT   12 app_fun

• Symbols “main” and “app_fun” are present in application binary file

• Hence we can confirm application is compiled successfully

Step 7.4: Check the “nm” output of the application binary file

Step 7.4.1: Check “nm” -S

• nm -S: Print both value and size of defined symbols for the “bsd” output style

• Check if “main” is present or not in the “nm”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm -S helloworld | grep -i main

00000000004004f0 0000000000000024 T main

What is “-S” option is used in “nm” command ?

See Answer

• -S: Print both value and size of defined symbols for the “bsd” output style

What “nm” command does ?

See Answer

• nm is used to dump the symbol table and their attributes from a binary executable file.

What is the purpose of “nm” command ?

See Answer

• The main purpose of the nm tool is to display information about symbols in the specified File, which can be an object file, an executable file, or an object-file library.

  • Check if “app_fun” is present or not in the “nm”

  $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm -S helloworld | grep -i app_fun
  
  00000000004005c0 000000000000000c T app_fun
  

• Symbols “main” and “app_fun” are present in application binary file

• Hence we can confirm application is compiled successfully

Step 7.4.2: Check “nm” -s

• nm -s: When listing symbols from archive members, include the index: a mapping of which modules contain definitions for which names.

• Check if “main” is present or not in the “nm”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm -s helloworld | grep -i main

00000000004004f0 T main

What is “-s” option is used in “nm” command ?

See Answer

• -s: When listing symbols from archive members, include the index: a mapping of which modules contain definitions for which names.

• Check if “app_fun” is present or not in the “nm”

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm -s helloworld | grep -i app_fun

00000000004005c0 T app_fun

• Symbols “main” and “app_fun” are present in application binary file

• Hence we can confirm application is compiled successfully

Step 7.5: Check the “file” command output of application binary file

• file: Determine file type

$ file helloworld

helloworld: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-aarch64.so.1, with debug_info, not stripped

Why “file” command is used ?

See Answer

• file command is used to determine the file type.

Step 7.6: Check the “size” command output of application binary file

• size: List section sizes and total size of binary files

$ size helloworld

  text    data     bss     dec     hex filename
  1190     648      56    1894     766 helloworld

What “size” command does ?

See Answer

• size command will display the output that will give you information on the size command in 5 values like data, text, dec, bss, and hex

Step 7.7: Check the “strings” command output of application binary file

• strings - print the sequences of printable characters in files

• As we can see string output are added in the program are confirmed.

$ strings helloworld | grep -i Hi

  Hi, application

What “strings” command does ?

See Answer

• strings command is used to return the string characters into files.

Step 7.8: Check the location of .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

$ ls -l | grep -i "helloworld"

 lrwxrwxrwx 1 sysadmin sysadmin 126 Jan  2 11:51 helloworld_1.0-1_aarch64_cortex-a72.ipk -> /home/test/openwrt/bin/packages/aarch64_cortex-a72/mypackages/helloworld_1.0-1_aarch64_cortex-a72.ipk

• ipk file: It is compressed archive format derived from the Debian package (. DEB) format

What is “IPK” file ?

See Answer

• IPK file is a compressed archive format derived from the Debian package (. DEB) format

Step 7.9: How to extract .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

• Command to extract .ipk file is below

$ tar -xzf helloworld_1.0-1_aarch64_cortex-a72.ipk

$ ls

  control.tar.gz
  data.tar.gz
  debian-binary

what is the command to extract IPK file ?

See Answer

• tar -xzf helloworld_1.0-1_aarch64_cortex-a72.ipk

Step 7.10: How to check content of .ipk file

• First extract control.tar.gz and data.tar.gz

• Command to check content for control.tar.gz file is below

$ tar -xzvf control.tar.gz

./control
./postinst
./prerm

• Check ./control using “vim command”

$ vim ./control

• Content of ./control

Package: helloworld
Version: 1.0-1
Depends: libc
Source: package/mypackages/examples/helloworld
SourceName: helloworld
Section: examples
SourceDateEpoch: 1703276774
Architecture: aarch64_cortex-a72
Installed-Size: 1244
Description:  A simple "Hello, world!" -application.

• Check inside for other files ./postinst and ./prerm using “vim” command

• Command to check content for control.tar.gz file is below

$ tar -xzvf data.tar.gz

 ./usr/
 ./usr/bin/
 ./usr/bin/helloworld

• Check ./usr/bin/helloworld is a binary file

Step 8: Build full openwrt - Incremental

In this section you will learn how to build full openwrt

Step 8.1: Do Pre-Build checks

• Make sure the current directory “openwrt”

$HOME/openwrt

Step 8.2: Build full openwrt

$ make -j1 V=s

• It compile all packages

• -j1: This option tells the build system work on one task at a time.

• V=s: This sets the verbosity level to ‘s’, which means “silent” or “verbose.” When set to ‘s’, it makes the build system display more detailed information about what it’s doing. You’ll see the commands it’s running and the files it’s working on. This verbose output is helpful for understanding and debugging the build process.

Step 8.3: Do Post-Build checks

Step 8.3.1 : Check the location of the full image

• Make sure the current directory “openwrt”

• To check package is successfully compiled, below is the path

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

• To check the image file is present or not

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin     1652 Jan  2 11:50 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin       83 Jan  2 11:50 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin 17117078 Jan  2 11:52 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 17117925 Jan  2 11:52 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin     4207 Jan  2 11:52 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin 15350996 Jan  2 11:52 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 15351843 Jan  2 11:52 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin     4096 Jan  2 11:52 packages
-rw-r--r-- 1 sysadmin sysadmin     2141 Jan  2 11:52 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      912 Jan  2 11:52 sha256sums
-rw-r--r-- 1 sysadmin sysadmin       18 Jan  2 11:50 version.buildinfo

• As we can see “image” is present then it is confirmed that fully image is successfull

• Image file is openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

Step 8.3.2 : How to extract full image file

• To extract image file command and pathis below

• Make sure the current directory “openwrt”

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin      1652 Jan  4 18:52 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin        83 Jan  4 18:52 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin  17117925 Jan  4 18:54 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin      4207 Jan  4 18:54 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin  15350996 Jan  4 18:54 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin  15351843 Jan  4 18:54 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin      4096 Jan  4 18:54 packages
-rw-r--r-- 1 sysadmin sysadmin      2141 Jan  4 18:54 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      1025 Jan  4 18:54 sha256sums
-rw-r--r-- 1 sysadmin sysadmin        18 Jan  4 18:52 version.buildinfo

• Command to extract full image file

$ gunzip -d openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

• After extracting image file check with ls command it will display below file

$ ls -l

 -rw-r--r-- 1 sysadmin sysadmin 184549376 Jan  4 18:54 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img

Step 8.3.3: Check the content of image file

• Content of full image file

• Check image file using “vim command”

$ vim openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img

• In vim openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img file search for binary file name (wait for a second)

• In this case binary file is helloworld

Step 8.3.4 : Check the size of the full image

• The du (disk usage) that allows users to analyze and report on disk usage within directories and files.

• Displays sizes in human-readable format, using units such as KB, MB, GB, etc.

  $ du -h openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
  
  17M     openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
  

• As we can see size of image file is around 17M