### Install elogind using Ninja

Source: https://github.com/elogind/elogind/blob/main/README.md

Install the built elogind components to their designated system locations using the Ninja build system.

```bash
sudo ninja install
```

--------------------------------

### Install elogind with a custom destination directory

Source: https://github.com/elogind/elogind/blob/main/README.md

Install elogind to a specific destination directory using the DESTDIR variable with the Ninja install command.

```bash
DESTDIR=... ninja install
```

--------------------------------

### Locate and Set LD_LIBRARY_PATH for Clang Sanitizer DSOs

Source: https://github.com/elogind/elogind/blob/main/docs/TESTING_WITH_SANITIZERS.md

After compiling with clang and `-shared-libsan`, binaries might complain about missing `libclang_rt.asan*` libraries. This example shows how to find the runtime DSO and set `LD_LIBRARY_PATH` to make it accessible.

```bash
# Optionally locate the respective runtime DSO
$ ldd build/elogind | grep libclang_rt.asan
        libclang_rt.asan-x86_64.so => not found
        libclang_rt.asan-x86_64.so => not found
$ find /usr/lib* /usr/local/lib* -type f -name libclang_rt.asan-x86_64.so 2>/dev/null
/usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so

# Set the LD_LIBRARY_PATH accordingly
export LD_LIBRARY_PATH=/usr/lib64/clang/7.0.1/lib/

# If the path is correct, the "not found" message should change to an actual path
$ ldd build/elogind | grep libclang_rt.asan
        libclang_rt.asan-x86_64.so => /usr/lib64/clang/7.0.1/lib/libclang_rt.asan-x86_64.so (0x00007fa9752fc000)
```

--------------------------------

### Function Parameter Naming Convention Example

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Illustrates the naming convention for function parameters, distinguishing between input, mutable, success return, and failure return parameters. Use 'ret_' prefix for success returns and 'reterr_' for failure returns.

```c
static int foobar_frobnicate(
                  Foobar *object,            /* the associated mutable object */
                  const char *input,         /* immutable input parameter */
                  char **ret_frobnicated,    /* return parameter on success */
                  unsigned *reterr_line,     /* return parameter on failure */
                  unsigned *reterr_column) { /* ditto */
          …
          return 0;
  }
```

--------------------------------

### Incorrect Order of Return Parameters

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Shows an example of an incorrect order for function parameters, where failure and success return parameters are not placed according to the specified convention.

```c
static int do_something(
                  const char *reterr_on_failure,
                  const char *ret_on_success,
                  const char *input);
```

--------------------------------

### Build elogind using Makefile wrapper

Source: https://github.com/elogind/elogind/blob/main/README.md

Use the Makefile for IDE compatibility (like CLion or VSCode). For maximum control, direct Meson/Ninja usage is recommended.

```bash
make DEBUG=YES
```

--------------------------------

### Build elogind using Meson and Ninja

Source: https://github.com/elogind/elogind/blob/main/README.md

Standard build command for elogind. It configures the build environment and then proceeds with the build using Ninja.

```bash
meson build/ && ninja -C build
```

--------------------------------

### Run all tests with Ninja

Source: https://github.com/elogind/elogind/blob/main/README.md

Execute all defined test suites for the elogind project using the Ninja build system.

```bash
ninja test
```

--------------------------------

### Run Unit Tests

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Execute unit tests using Meson. Consider running with sudo for tests requiring privileges, or with specific flags for unsafe or slow tests. Flags can be configured for existing build trees.

```bash
meson test -C build
sudo meson test -C build
meson setup -Dtests=unsafe
meson setup -Dslow-tests=true
meson configure -C build -D...
```

--------------------------------

### Change elogind configuration options

Source: https://github.com/elogind/elogind/blob/main/README.md

After initial configuration, use this command to modify build arguments. Running `meson configure` without arguments lists available options.

```bash
meson configure -Darg=value... build/
```

--------------------------------

### Run Integration Tests

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Execute the full integration test suite, which involves building OS images and running tests.

```bash
./test/run-integration-tests.sh
```

--------------------------------

### Configure mkosi for Sanitizers

Source: https://github.com/elogind/elogind/blob/main/docs/TESTING_WITH_SANITIZERS.md

Add this configuration to `mkosi.local.conf` to enable Address and Undefined Behavior Sanitizers when building with mkosi. This passes the sanitizers option to meson's `b_sanitize`.

```ini
[Content]
Environment=SANITIZERS=address,undefined
```

--------------------------------

### Configure 'video' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'video' group. Use this option to specify a custom GID.

```meson
# option('video-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "video" group')
```

--------------------------------

### Debugging systemd-homed with Environment Variables

Source: https://github.com/elogind/elogind/blob/main/docs/ENVIRONMENT.md

This snippet demonstrates how to run an additional copy of systemd-homed for debugging or development purposes by setting specific environment variables. These variables control debug suffixes, homework paths, root directories, and record directories.

```sh
SYSTEMD_HOME_DEBUG_SUFFIX=foo \
      SYSTEMD_HOMEWORK_PATH=/home/lennart/projects/systemd/build/systemd-homework \
      SYSTEMD_HOME_ROOT=/home.foo/ \
      SYSTEMD_HOME_RECORD_DIR=/var/lib/systemd/home.foo/ \
      /home/lennart/projects/systemd/build/systemd-homed
```

--------------------------------

### Check API Documentation

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Compare exported symbols of shared libraries with man pages to identify undocumented symbols. This command requires a Meson-built tree.

```bash
ninja -C build check-api-docs
```

--------------------------------

### Update Hardware Database

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Automatically download and import PCI, USB, and OUI databases, as well as autosuspend quirks, into the hardware database. This command requires a Meson-built tree.

```bash
ninja -C build update-hwdb
ninja -C build update-hwdb-autosuspend
```

--------------------------------

### Run a specific target with Ninja

Source: https://github.com/elogind/elogind/blob/main/README.md

Execute a particular build target defined in the Ninja build system.

```bash
ninja -v some/target
```

--------------------------------

### Use EXIT_SUCCESS and EXIT_FAILURE for main return

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

When returning a status code from the main() function, prefer using EXIT_SUCCESS and EXIT_FAILURE as defined by libc for clarity and portability.

```c
return EXIT_SUCCESS;
```

--------------------------------

### Configure 'systemd-resolve' user UID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the systemd-resolve user. Use this option to specify a custom UID.

```meson
# option('systemd-resolve-uid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the systemd-resolve user')
```

--------------------------------

### Build a static version of libelogind

Source: https://github.com/elogind/elogind/blob/main/README.md

Add this Meson option during configuration to build a static library alongside the shared library. Options include 'pic', 'true', or 'no-pic'.

```bash
-Dstatic-libelogind=pic
```

--------------------------------

### Configure 'tape' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'tape' group. Use this option to specify a custom GID.

```meson
# option('tape-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "tape" group')
```

--------------------------------

### Create an elogind tarball

Source: https://github.com/elogind/elogind/blob/main/README.md

Command to create a compressed tar archive of the elogind source code from a git repository.

```bash
git archive --format=tar --prefix=elogind-241/ v241 | xz > elogind-241.tar.xz
```

--------------------------------

### Configure 'systemd-timesync' user UID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the systemd-timesync user. Use this option to specify a custom UID.

```meson
# option('systemd-timesync-uid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the systemd-timesync user')
```

--------------------------------

### Configure 'utmp' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'utmp' group. Use this option to specify a custom GID.

```meson
# option('utmp-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "utmp" group')
```

--------------------------------

### Configure 'systemd-network' user UID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the systemd-network user. Use this option to specify a custom UID.

```meson
# option('systemd-network-uid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the systemd-network user')
```

--------------------------------

### Configure 'lp' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'lp' group. Use this option to specify a custom GID.

```meson
# option('lp-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "lp" group')
```

--------------------------------

### Configure 'users' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'users' group. Use this option to specify a custom GID.

```meson
# option('users-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "users" group')
```

--------------------------------

### Update Man Page Rules

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Update the Meson rules for automatically building man pages from docbook XML files. This command requires a Meson-built tree.

```bash
ninja -C build update-man-rules
```

--------------------------------

### Configure 'render' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'render' group. Use this option to specify a custom GID.

```meson
# option('render-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "render" group')
```

--------------------------------

### Configure elogind with a specific cgroup controller

Source: https://github.com/elogind/elogind/blob/main/README.md

Use this option when the target init system and cgroup controller are not yet active during the build process. It informs elogind which controller will be in charge.

```bash
--with-cgroup-controller=openrc
```

--------------------------------

### Correct Order of Return Parameters

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Demonstrates the preferred order for function parameters, placing failure return parameters (`reterr_`) last and success return parameters (`ret_`) immediately before them.

```c
static int do_something(
                  const char *input,
                  const char *ret_on_success,
                  const char *reterr_on_failure);
```

--------------------------------

### Runtime Sanitizer Options for GCC/Clang

Source: https://github.com/elogind/elogind/blob/main/docs/TESTING_WITH_SANITIZERS.md

Set these environment variables to configure the runtime behavior of Address Sanitizer and Undefined Behavior Sanitizer for more useful debugging output. These are used after compiling with `-Db_sanitize=address,undefined`.

```bash
ASAN_OPTIONS=strict_string_checks=1:detect_stack_use_after_return=1:check_initialization_order=1:strict_init_order=1
UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
```

--------------------------------

### Function Definition Style

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Prefer defining functions with the opening brace on the same line as the function signature.

```c
void foo() {
}

```

--------------------------------

### Configure 'systemd-journal' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the systemd-journal group. Use this option to specify a custom GID.

```meson
# option('systemd-journal-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the systemd-journal group')
```

--------------------------------

### C Structure Initialization with Initializers

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use C99 structure initializers for initializing stack-allocated structs instead of memzero() or memset(). This is shorter, cleaner, and faster.

```c
struct foobar t = {
        .foo = 7,
        .bar = "bazz",
};

```

```c
struct foobar t;
zero(t);
t.foo = 7;
t.bar = "bazz";

```

--------------------------------

### Configure 'sgx' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'sgx' group. Use this option to specify a custom GID.

```meson
# option('sgx-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "sgx" group')
```

--------------------------------

### Configure 'wheel' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the soft-static allocation for the 'wheel' group. Use this option to specify a custom GID.

```meson
# option('wheel-gid', type : 'integer', value : 0,
#        description : 'soft-static allocation for the "wheel" group')
```

--------------------------------

### Using Safe Memory Allocation Wrappers

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Prefer safe wrappers like alloca_safe(), strdupa_safe(), and strndupa_safe() over their direct counterparts. These wrappers include safety assertions to prevent stack overruns.

```c
alloca_safe()
```

```c
strdupa_safe()
```

```c
strndupa_safe()
```

--------------------------------

### Else Block Formatting

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Place the 'else' keyword on the same line as the closing brace of the preceding 'if' block.

```c
if (foobar) {
        find();
        waldo();
} else
        dont_find_waldo();

```

--------------------------------

### C Variable Declaration and Initialization

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Declare local variables at the top of a block or where they can be initialized. Avoid large declaration lists. 'int r' is an exception for state variables.

```c
{
        uint64_t a;
        int r;

        r = frobnicate(&a);
        if (r < 0)
                …

        uint64_t b = a + 1, c;

        r = foobarify(a, b, &c);
        if (r < 0)
                …

        const char *pretty = prettify(a, b, c);
        …
}
```

--------------------------------

### Combined Log and Return Operation

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use this pattern for operations that should log errors and return the error code. It simplifies error handling by combining the operation, check, and logging into a single statement.

```c
r = operation(...);
if (r < 0)
        return log_(error|warning|notice|...)_errno(r, "Failed to ...: %m");
```

--------------------------------

### Compile with Shared Sanitizer Libraries for Clang

Source: https://github.com/elogind/elogind/blob/main/docs/TESTING_WITH_SANITIZERS.md

When using clang, pass `-shared-libasan` to CFLAGS and CXXFLAGS to ensure sanitizer libraries are linked dynamically. This is crucial for integration tests when an instrumented library is loaded by a standard application.

```bash
CFLAGS=-shared-libasan
CXXFLAGS=-shared-libasan
```

--------------------------------

### Run Coccinelle Semantic Patch Scripts

Source: https://github.com/elogind/elogind/blob/main/docs/CODE_QUALITY.md

Execute all provided Coccinelle semantic patch scripts. Note that the output may contain false positives.

```bash
./coccinelle/run-coccinelle.sh
```

--------------------------------

### Safe Stack String Allocation

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

When allocating fixed-size strings on the stack, use standard macros like LINE_MAX or count the maximum size carefully. Avoid arbitrary small buffer sizes like char buf[256].

```c
char buf[256]
```

--------------------------------

### Enum for Public API Size Enforcement

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use the _SD_ENUM_FORCE_S64() macro in public API enum definitions to ensure a consistent 64-bit size and maintain ABI compatibility.

```c
#define _SD_ENUM_FORCE_S64() // Forces the size of the enum to be signed 64-bit wide.

```

--------------------------------

### C Yoda Comparison Style

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Prefer readable comparisons like 'if (a == 7)' over less readable Yoda comparisons like 'if (7 == a)'.

```c
if (a == 7)
```

```c
if (7 == a)
```

--------------------------------

### String Concatenation with strjoina or strjoin

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

For concatenating multiple strings, use strjoina() or strjoin() instead of asprintf() for better performance, especially in loops. Note that strjoina() is not suitable for inner loops.

```c
strjoina()
```

```c
strjoin()
```

--------------------------------

### Function Return Type Formatting

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Define function return types as a whole, attached to the function name, rather than on a separate line.

```c
const char* foo(const char *input);

```

--------------------------------

### C Boolean Conversion Check

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use C's downgrade-to-bool feature for expressions that are actually booleans. For numeric variables with more than two semantic values, explicitly check for non-zero using '!= 0' for clarity.

```c
if (b)
```

```c
if (b != 0)
```

--------------------------------

### Code Block Separation and Error Handling

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use single empty lines to separate code blocks. Avoid empty lines between function calls and their immediate error handling.

```c
/* → empty line here is good */
r = some_function(…);
/* → empty line here would be bad */
if (r < 0)
        return log_error_errno(r, "Some function failed: %m");
/* → empty line here is good */

```

--------------------------------

### Configure 'tty' group GID

Source: https://github.com/elogind/elogind/blob/main/meson_options.txt

Sets the numeric GID of the 'tty' group. The default value is 5.

```meson
# option('tty-gid', type : 'integer', value : 5,
#        description : 'the numeric GID of the "tty" group')
```

--------------------------------

### Convert libc error to elogind style

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use the RET_NERRNO() helper to convert libc-style error returns (-1 with errno) to elogind's negative error code style. This is useful for system calls like unlink() and open().

```c
r = RET_NERRNO(unlink(t));
```

```c
r = RET_NERRNO(open("/some/file", O_RDONLY|O_CLOEXEC));
```

--------------------------------

### Function Declaration Formatting

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

When breaking a function declaration over multiple lines, use double indentation for the parameter list.

```c
void some_function(
                  int foo,
                  bool bar,
                  char baz) {

        int a, b, c;

```

--------------------------------

### C Infinite Loop Construct

Source: https://github.com/elogind/elogind/blob/main/docs/CODING_STYLE.md

Use 'for (;;)' for endless loops instead of 'while (1)' or 'while (true)' to avoid discussions about the correct always-true expression.

```c
for (;;)
```