Diff — Building from Source

{{infobox

| title = Building from Source

| chapter = Linux Handbook, chapter 16 — tarballs, configure/make/install, build systems, patching

| core | The ./configure && make && make install liturgy — and what each step does

| systems | autotools · cmake · meson/ninja · plain makefiles

| skills | configure flags · DESTDIR/prefix · patches · out-of-tree builds

| next | Inside a Linux system — what a built system consists of

}}

**Building from source is the original Linux distribution mechanism** — before package managers, you got software as a tarball, configured it for your system, compiled it, and installed it. Every LFS chapter is this ritual repeated; every BLFS package, every `git clone` project, every ancient tarball in an archive.org listing runs the same liturgy. This chapter teaches the liturgy and the build systems that automate it — the universal grammar of "source → installed".

## The liturgy — three sacred steps

```sh

tar -xf package-1.0.tar.xz

cd package-1.0

./configure --prefix=/usr      # adapt the build to THIS system

make -j$(nproc)                # compile

make check                     # optional testsuite

sudo make install              # install

```

**`configure`** probes the system — compiler present? headers? libraries? — and generates the Makefiles. **`make`** builds per the Makefile. **`make install`** copies binaries, headers, libraries, docs into `--prefix`. Three steps; a hundred years of software follows them.

## configure — the system's interrogation

```sh

./configure --help             # every package's custom options

./configure --prefix=/usr \    # WHERE it installs — the big one

            --sysconfdir=/etc \# config location

            --localstatedir=/var \

            --disable-static \  # don't ship .a libraries

            --enable-shared \

            --with-foo --without-bar   # feature toggles

```

`--prefix` decides *where everything lands*: `/usr` (system), `/usr/local` (local additions, the classic default), `/opt/package` (self-contained). The LFS prefix dance — `/tools`, `/usr`, `DESTDIR` — is this flag doing deep work.

**`make DESTDIR=$STAGING install`** — the packager's trick: install *believing* prefix is `/usr` but landing in `$STAGING/usr` — how packages get built for one root and assembled for another.

## The other build systems

| System | Liturgy | Found in |

| --- | --- | --- |

| **autotools** | `./configure && make && make install` | The classic — most tarballs |

| **cmake** | `cmake -B build -DCMAKE_INSTALL_PREFIX=/usr && cmake --build build` | KDE, modern C++ |

| **meson** | `meson setup build --prefix=/usr && ninja -C build` | GNOME, systemd-era |

| **plain make** | `make && make install` | Minimal projects |

| **cargo/go/npm** | the language's own | Rust, Go, Node projects |

cmake's `-B build` creates an **out-of-tree build dir** — the modern way; source tree stays pristine. Meson+ninja is the fastest. Autotools remains the most common on old-school tarballs — and the deepest to understand: `configure.ac` → `autoconf` → `configure` → `Makefile.in` → `make`.

## What configure actually detects

```sh

./configure ... 2>&1 | tee config.log     # keep the log — failures live there

tail -20 config.log                        # when it fails, the answer's here

```

`configure` compiles test programs — "checking for gcc... yes" means it ran a hello-world; "checking for foo.h... no" means a test compile failed. The fix is almost always a **missing -dev/-devel package**: `libfoo-dev` supplies the headers a build needs that the runtime `libfoo` doesn't. Debian's `-dev`, Red Hat's `-devel`, Slackware ships headers always — the host difference.

## Patches — the surgical fixes

```sh

patch -p1 < fix.patch          # apply — -p1 strips the a/ b/ prefixes

patch -R -p1 < fix.patch       # reverse — the undo

diff -u old.c new.c > my.patch # create one

diff -Naur old/ new/ > big.patch  # whole trees

```

LFS's build applies dozens of small patches — FHS placements, security fixes, cross-build fixes — each a surgical diff that upstream hasn't folded in yet.

## The configure internals — what it actually runs

```sh

./configure --help | less               # every option the package ships

cat config.log                          # the probe transcript — failures live here

less config.status                      # the record of what was detected

cat config.h                            # the generated feature macros

```

`configure` is a generated shell script — thousands of small test-compiles: "checking for gcc... yes" means it ran a hello-world; "checking foo.h usability... no" means a test compile failed and the config.log shows the *compiler's actual error*. `config.status --recheck` reruns; `config.status` regenerates the Makefiles.

## The DESTDIR/prefix grammar — the packager's two knobs

```sh

./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var

make

make install                        # writes to /usr, /etc — REAL

# vs:

make DESTDIR=/tmp/stage install     # writes to /tmp/stage/usr — STAGED

```

`--prefix` = where the software *believes* it lives (baked into paths); `DESTDIR` = where it *actually lands* (the packager's staging). LFS uses both — `--prefix=/usr` + `DESTDIR=$LFS` = "believe /usr, land in $LFS/usr" — exactly where the chroot needs it. The `--sysconfdir`/`--localstatedir` pair move `/etc` and `/var` away from `/usr/etc`/`/usr/var` (the classic wrong defaults).

## The meson + cmake grammar

```sh

# meson — the modern fast one

meson setup build --prefix=/usr --buildtype=release -Dfeature=enabled

ninja -C build

ninja -C build test

DESTDIR=/tmp/stage ninja -C build install

meson configure build -Doption=value   # reconfigure

# cmake — the heavyweight

cmake -B build -DCMAKE_BUILD_TYPE=Release \

      -DCMAKE_INSTALL_PREFIX=/usr \

      -DBUILD_TESTING=OFF -DWITH_X=ON

cmake --build build -j$(nproc)

cmake --install build --prefix /tmp/stage/usr

ctest --test-dir build                 # the tests

```

Both honor `DESTDIR`; meson's `-D` toggles the package's own options (`meson_options.txt` lists them); cmake's `-DWITH_*`/`-DBUILD_*` the same.

## Dependencies — the real work

The tarball itself is the easy half; the dependencies are the job:

```sh

./configure   # missing dep = the error is your answer

apt build-dep package        # Debian's dep-fetcher — installs every build-dep

ldd binary | grep 'not found' # runtime gaps

pkg-config --modversion foo  # is it visible to builds?

```

`apt build-dep`, `dnf builddep`, Slackware's "install everything" — each distro's answer to "install the deps this needs". On LFS, dependency management *is* the book's ordering — the build sequence is topological.

## Version sanity and the release hygiene

```sh

make V=1                      # verbose builds — the actual commands

./configure --version         # sometimes tells you what's expected

cat README INSTALL NEWS       # the three files always worth a skim

```

And the trust layer: `gpg --verify package.tar.xz.sig package.tar.xz`, `md5sum`/sha256 checks — the sources are the system's DNA; verify before compiling. This handbook's LFS chapters verify checksums before the first configure — chapter 2 makes it law.

## The install aftermath

```sh

make install DESTDIR=$D       # staged install — packager's form

make install                  # real install — needs root for /usr

ldconfig                      # refresh the .so registry after new libs

command -v newtool            # did it land in PATH?

make uninstall                # often supported — often doesn't exist

```

`checkinstall`/`make install` into `/usr/local` keeps hand-built software quarantined from the package manager's `/usr` — the classic hygiene.

## Where source builds go wrong

| Symptom | Cause |

| --- | --- |

| `configure: foo.h not found` | Missing `-dev`/`devel` package |

| `config.log` cryptic failure | Read the last 20 lines — always |

| Installed but `command not found` | `--prefix` landed outside PATH — `/usr/local/bin`? |

| `libtool` version fights | The tarball's ltmain vs the host's — `autoreconf -fi` |

| Build works, install fails on perms | `sudo make install` — or DESTDIR staging |

| Old build residue breaks rebuild | `make distclean` — or re-extract fresh |

| `make` fails only parallel | Racy Makefile — `-j1` |

| .la files breaking downstream | `rm` the `.la` files — libtool's legacy hazard |

## Exercises

1. Build a real tarball — `tar`, `configure`, `make`, DESTDIR-staged install into `/tmp/stage`.

2. `tee` a configure log; find the exact probe that failed for a missing lib.

3. `apt build-dep` or `dnf builddep` something — see the dep list as a set.

4. Write and apply a patch — `diff -u`, `patch -p1`, then `patch -R` it back.

5. Compare a cmake and an autotools build side by side — the different liturgies.

## See also

- [[C toolchain]] · [[LFS Cross-Toolchain]] · [[LFS System Packages]] · [[Linux]]

[[Category:Linux]]

[[Category:Handbook]]

[[Category:Compilers]]