How to use gdb in Ubuntu Terminal

Here's a practical, minimal guide for using GDB in Ubuntu terminal — from launching to setting breakpoints and navigating your code.

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🧰 Step 1: Compile with Debug Symbols

Use -g and disable optimizations (-O0 preferred for debugging):

bash
g++ -g -O0 -o myprog myprog.cpp

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🚀 Step 2: Launch GDB

bash
gdb ./myprog

You'll see a (gdb) prompt.

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🎯 Step 3: Set Breakpoints

You can set breakpoints in three main ways:

✅ a. At a function

gdb
(gdb) break main

✅ b. At a specific file and line

gdb
(gdb) break myprog.cpp:42

✅ c. At a method in a class

gdb
(gdb) break MyClass::doSomething

If the symbol is mangled (C++), GDB usually demangles automatically, especially if compiled with -g.

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▶️ Step 4: Run the Program

gdb
(gdb) run

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🧭 Step 5: Navigate

Command	Meaning
next or n	Step over current line
step or s	Step into function call
finish	Run until current function returns
continue or c	Continue until next breakpoint
list	Show source code around current line
info locals	Show all local variables
print x	Print variable x

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⛏️ Step 6: Manage Breakpoints

List breakpoints:

gdb
(gdb) info breakpoints

Delete a breakpoint:

gdb
(gdb) delete <number>

Disable/Enable breakpoint temporarily:

gdb
(gdb) disable <number>
(gdb) enable <number>

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🧪 Example Session

bash
g++ -g -O0 -o test test.cpp
gdb ./test

gdb
(gdb) break main
(gdb) break test.cpp:18
(gdb) run
(gdb) next
(gdb) print myVar
(gdb) continue

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🧠 Pro Tips

• Press <TAB> for autocompletion.

• Use layout src in GDB to get a TUI (text UI).

• quit to exit.

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🪟 Bonus: GDB Text UI Mode

In GDB:

gdb
(gdb) layout src

→ Shows source code window with current line highlighted. Use arrow keys or n, s, etc.

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Let me know if you'd like:

• Watchpoints (for memory change)

• Debugging core dumps

• Pretty printing with gdbinit

• Automating GDB session with scripts

Install gcc 15.1 using spack in Ubuntu (chatGpt Reply)

git clone https://github.com/spack/spack.git ~/spack

. ~/spack/share/spack/setup-env.sh

spack install [email protected]

spack load [email protected]

Install gcc-15.1 form source in Ubuntu (chatGpt reply)

✅ Step-by-step: Build and Install GCC 15.1 on Ubuntu

⚠️ Estimated time: ~30–60 mins
✅ Works on Ubuntu 20.04 / 22.04 / 24.04

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1. Install dependencies

bash
sudo apt update
sudo apt install -y build-essential wget curl git \
  libgmp-dev libmpfr-dev libmpc-dev libisl-dev \
  flex bison libzstd-dev

2. Download GCC 15.1 source
bash
cd ~/Downloads
wget https://ftp.gnu.org/gnu/gcc/gcc-15.1.0/gcc-15.1.0.tar.xz
tar -xf gcc-15.1.0.tar.xz
cd gcc-15.1.0
./contrib/download_prerequisites


This will fetch GMP, MPFR, MPC, and ISL into the source tree.


3. Create build directory
bash
mkdir ../gcc-15.1-build
cd ../gcc-15.1-build


4. Configure build
bash
../gcc-15.1.0/configure \
  --prefix=/opt/gcc-15.1 \
  --disable-multilib \
  --enable-languages=c,c++,fortran \
  --enable-bootstrap \
  --enable-checking=release


5. Build (takes time)
bash
make -j$(nproc)


6. Install
bash
sudo make install

7. Use GCC 15.1
Add it to your shell:
bash
echo 'export PATH=/opt/gcc-15.1/bin:$PATH' >> ~/.bashrc
echo 'export LD_LIBRARY_PATH=/opt/gcc-15.1/lib64:$LD_LIBRARY_PATH' >> ~/.bashrc
source ~/.bashrc


8. Check version
bash
gcc --version

Should show:
scss
gcc (GCC) 15.1.0


✅ Optional: Set it system-wide (alternative)
Update update-alternatives if you want it globally:
bash
sudo update-alternatives --install /usr/bin/gcc gcc /opt/gcc-15.1/bin/gcc 1501
sudo update-alternatives --install /usr/bin/g++ g++ /opt/gcc-15.1/bin/g++ 1501

Then run:
bash
sudo update-alternatives --config gcc
sudo update-alternatives --config g++