diff --git a/cmd/shutdown.c b/cmd/shutdown.c
index 16e0c8e..0d11cc5 100644
--- a/cmd/shutdown.c
+++ b/cmd/shutdown.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <getopt.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/initd/init.h b/initd/init.h
index 0bfed6c..dee0b00 100644
--- a/initd/init.h
+++ b/initd/init.h
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #ifndef INIT_H
 #define INIT_H
 
@@ -14,22 +31,101 @@ enum {
 	STATUS_WAIT,
 };
 
+/********** runlst.c **********/
+
+/*
+	Plow through an array of strings and execute each one, i.e. do
+	a fork() and exec().
+
+	In the parent process, wait() until the child is done before
+	continuing through the list.
+
+	If ctty is not NULL, open it and redirect all I/O of the child
+	process to that file.
+
+	If everyhing works, the function returns EXIT_SUCCESS. If one child
+	does not exit with EXIT_SUCCESS, processing of the list is aborted
+	and the function returns the exit status of the failed process.
+*/
 int runlst_wait(char **exec, size_t num, const char *ctty);
 
+/*
+	Does basically the same as runlst_wait, but asynchronously.
+
+	A child process is created that calls runlst_wait exits with the
+	result of runlst_wait. In the parent process, the function returns
+	immediately with the PID of the child process.
+
+	Alternatively, if num is 1, the child process directly exec()s the
+	given command.
+*/
 pid_t runlst(char **exec, size_t num, const char *ctty);
 
+/********** setup_tty.c **********/
+
+/*
+	Initial tty setup for init. Makes /dev/console our controlling tty and
+	reroutes all output there. Closes stdin because we presumably won't
+	need it anymore.
+
+	Returns 0 on success, -1 on failure. The function takes care of
+	printing error messages on failure.
+*/
 int setup_tty(void);
 
+/********** status.c **********/
+
+/*
+	Print a status message. Type is either STATUS_OK, STATUS_FAIL or
+	STATUS_WAIT.
+
+	A new-line is appended to the mssage, UNLESS type is STATUS_WAIT.
+
+	If update is true, print a carriage return first to overwrite the
+	current line (e.g. after a STATUS_WAIT message).
+*/
 void print_status(const char *msg, int type, bool update);
 
+/********** mksock.c **********/
+
+/*
+	Create a UNIX socket that programs can use to pass messages to init.
+
+	Returns the socked fd or -1 on failure. The function takes care of
+	printing error messages on failure.
+
+	The socket has the CLOEXEC flag set.
+*/
 int mksock(void);
 
+/********** shutdown.c **********/
+
+/*
+	Kindly tell all processes to go kill themselves, then send
+	a SIGKILL if they don't and perform system shutdown.
+
+	The argument is passed directly to the reboot() syscall.
+*/
 NORETURN void do_shutdown(int type);
 
+/********** svclist.c **********/
+
+/*
+	Returns true if the list of running services contains
+	single shot processes.
+*/
 bool svclist_have_singleshot(void);
 
+/* Add a service to the list of running services */
 void svclist_add(service_t *svc);
 
+/*
+	Remove a service, identifierd by PID, from the list of
+	running services.
+
+	Returns the service identified by the PID or NULL if there
+	is no such service.
+*/
 service_t *svclist_remove(pid_t pid);
 
 #endif /* INIT_H */
diff --git a/initd/main.c b/initd/main.c
index 211188e..be9fc0d 100644
--- a/initd/main.c
+++ b/initd/main.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
diff --git a/initd/mksock.c b/initd/mksock.c
index ab26e51..6a9cab0 100644
--- a/initd/mksock.c
+++ b/initd/mksock.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
diff --git a/initd/runlst.c b/initd/runlst.c
index cf75126..908ec15 100644
--- a/initd/runlst.c
+++ b/initd/runlst.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/wait.h>
 #include <signal.h>
 #include <unistd.h>
diff --git a/initd/setup_tty.c b/initd/setup_tty.c
index cec663b..807b69d 100644
--- a/initd/setup_tty.c
+++ b/initd/setup_tty.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <unistd.h>
 #include <fcntl.h>
 #include <stdio.h>
diff --git a/initd/shutdown.c b/initd/shutdown.c
index 45af1c2..1ee68c2 100644
--- a/initd/shutdown.c
+++ b/initd/shutdown.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
diff --git a/initd/status.c b/initd/status.c
index 280670b..67b049b 100644
--- a/initd/status.c
+++ b/initd/status.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdio.h>
 
 #include "init.h"
diff --git a/initd/svclist.c b/initd/svclist.c
index 590091e..4ed897f 100644
--- a/initd/svclist.c
+++ b/initd/svclist.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include "init.h"
 
 static service_t *running = NULL;	/* currently supervised services */
diff --git a/lib/include/service.h b/lib/include/service.h
index eb92d85..6808bdd 100644
--- a/lib/include/service.h
+++ b/lib/include/service.h
@@ -1,19 +1,45 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #ifndef SERVICE_H
 #define SERVICE_H
 
 #include <sys/types.h>
 
 enum {
+	/*
+		Start the service in the background and continue with
+		other services. The service will eventually terminate.
+	*/
 	SVC_ONCE = 0,
-	SVC_WAIT,
+	SVC_WAIT,		/* run service and wait until it finishes */
+
+	/*
+		Similar to SVC_ONCE, but restart the service when
+		it terminates.
+	*/
 	SVC_RESPAWN,
 };
 
 enum {
-	TGT_BOOT = 0,
-	TGT_SHUTDOWN,
-	TGT_REBOOT,
-	TGT_CAD,
+	TGT_BOOT = 0,		/* run service when the system boots */
+	TGT_SHUTDOWN,		/* run service when at system shut down */
+	TGT_REBOOT,		/* run service when during system reboot */
+	TGT_CAD,		/* run service when CTRL+ALT+DEL is pressed */
 
 	TGT_MAX
 };
@@ -27,9 +53,9 @@ typedef struct service_t {
 	size_t num_exec;	/* number of command lines */
 	char *ctty;		/* controlling tty or log file */
 
-	char **before;
+	char **before;		/* services that must be executed later */
 	size_t num_before;
-	char **after;
+	char **after;		/* services that must be executed first */
 	size_t num_after;
 
 	pid_t pid;
@@ -49,6 +75,13 @@ service_t *rdsrv(int dirfd, const char *filename);
 
 void delsrv(service_t *srv);
 
+/*
+	Rebuild a service list by scanning a directory and parsing all
+	service descriptions.
+
+	Returns 0 on success, -1 on failure. The function takes care of
+	printing error messages on failure.
+*/
 int srvscan(const char *directory, service_list_t *list);
 
 void del_srv_list(service_list_t *list);
diff --git a/lib/include/telinit.h b/lib/include/telinit.h
index 72ad871..3a3dd8c 100644
--- a/lib/include/telinit.h
+++ b/lib/include/telinit.h
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #ifndef TELINIT_H
 #define TELINIT_H
 
@@ -11,9 +28,10 @@ enum {
 };
 
 typedef struct {
-	int type;
+	int type;	/* TI_* message type identifier */
 } ti_msg_t;
 
+/* Try to connect to the init socket. */
 int opensock(void);
 
 #endif /* TELINIT_H */
diff --git a/lib/include/util.h b/lib/include/util.h
index bed2ba7..ed5dac2 100644
--- a/lib/include/util.h
+++ b/lib/include/util.h
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #ifndef UTIL_H
 #define UTIL_H
 
@@ -52,6 +69,11 @@ int splitkv(char *line, char **key, char **value);
 */
 const enum_map_t *enum_by_name(const enum_map_t *map, const char *name);
 
+/*
+	Create a copy of the input string inp, but replace all occourances
+	of %<number> with argv[number] if the number is within the bounds
+	specified by argc.
+*/
 char *strexpand(const char *inp, size_t argc, const char *const *argv);
 
 #endif /* UTIL_H */
diff --git a/lib/src/del_srv_list.c b/lib/src/del_srv_list.c
index 916fcb2..d54c40b 100644
--- a/lib/src/del_srv_list.c
+++ b/lib/src/del_srv_list.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdlib.h>
 
 #include "service.h"
diff --git a/lib/src/delsrv.c b/lib/src/delsrv.c
index b660558..87b65bc 100644
--- a/lib/src/delsrv.c
+++ b/lib/src/delsrv.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdlib.h>
 
 #include "service.h"
diff --git a/lib/src/enum_by_name.c b/lib/src/enum_by_name.c
index 1948eb9..95f306f 100644
--- a/lib/src/enum_by_name.c
+++ b/lib/src/enum_by_name.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <string.h>
 
 #include "util.h"
diff --git a/lib/src/opensock.c b/lib/src/opensock.c
index 06101ef..0c2bf56 100644
--- a/lib/src/opensock.c
+++ b/lib/src/opensock.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/un.h>
diff --git a/lib/src/rdline.c b/lib/src/rdline.c
index 591c713..1b91008 100644
--- a/lib/src/rdline.c
+++ b/lib/src/rdline.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdlib.h>
 #include <unistd.h>
 #include <errno.h>
diff --git a/lib/src/rdsrv.c b/lib/src/rdsrv.c
index 52eb19c..ec60ce1 100644
--- a/lib/src/rdsrv.c
+++ b/lib/src/rdsrv.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
diff --git a/lib/src/splitkv.c b/lib/src/splitkv.c
index 6c6fe94..b1ef8d3 100644
--- a/lib/src/splitkv.c
+++ b/lib/src/splitkv.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <ctype.h>
 
 #include "util.h"
diff --git a/lib/src/srv_tsort.c b/lib/src/srv_tsort.c
index e2549b1..d375c4f 100644
--- a/lib/src/srv_tsort.c
+++ b/lib/src/srv_tsort.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdbool.h>
 #include <stddef.h>
 #include <string.h>
diff --git a/lib/src/srvscan.c b/lib/src/srvscan.c
index 71ad4f9..69d0b91 100644
--- a/lib/src/srvscan.c
+++ b/lib/src/srvscan.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <stddef.h>
diff --git a/lib/src/strexpand.c b/lib/src/strexpand.c
index 7e552eb..58b69a0 100644
--- a/lib/src/strexpand.c
+++ b/lib/src/strexpand.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
diff --git a/servicecmd/disable.c b/servicecmd/disable.c
index 90d8b80..1901381 100644
--- a/servicecmd/disable.c
+++ b/servicecmd/disable.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <stdlib.h>
diff --git a/servicecmd/enable.c b/servicecmd/enable.c
index 8e6200c..73ea01e 100644
--- a/servicecmd/enable.c
+++ b/servicecmd/enable.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <stdlib.h>
diff --git a/servicecmd/help.c b/servicecmd/help.c
index 6cd816e..4fa9951 100644
--- a/servicecmd/help.c
+++ b/servicecmd/help.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include "servicecmd.h"
 
 extern char *__progname;
diff --git a/servicecmd/list.c b/servicecmd/list.c
index 2286197..aad70d6 100644
--- a/servicecmd/list.c
+++ b/servicecmd/list.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include "servicecmd.h"
 #include "service.h"
 #include "config.h"
diff --git a/servicecmd/servicecmd.c b/servicecmd/servicecmd.c
index 278afaf..ff37740 100644
--- a/servicecmd/servicecmd.c
+++ b/servicecmd/servicecmd.c
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #include <stdlib.h>
 #include <stdio.h>
 
diff --git a/servicecmd/servicecmd.h b/servicecmd/servicecmd.h
index ce5e58f..27204d0 100644
--- a/servicecmd/servicecmd.h
+++ b/servicecmd/servicecmd.h
@@ -1,3 +1,20 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
 #ifndef SERVICECMD_H
 #define SERVICECMD_H
 
@@ -8,21 +25,46 @@
 
 #include "util.h"
 
+/*
+	Describes a command that can be launched by passing its name as
+	second command line argument to the main() function (i.e. immediately
+	after the actual program name).
+
+	Short and long descriptions can be provided to print out help text.
+
+	The main() function calls into a callback in this structure to execute
+	the command.
+*/
 typedef struct command_t {
 	struct command_t *next;
 
-	const char *cmd;
-	const char *usage;
-	const char *s_desc;
-	const char *l_desc;
+	const char *cmd;	/* command name */
+	const char *usage;	/* list of possible arguments */
+	const char *s_desc;	/* short description used by help */
+	const char *l_desc;	/* long description used by help */
 
+	/*
+		Semantics are the same as for main(). Called from main()
+		function with first argument (i.e. top level program name)
+		removed.
+	*/
 	int (*run_cmd)(int argc, char **argv);
 } command_t;
 
+/* Global list of available commands */
 extern command_t *commands;
 
+/*
+	Implemented in servicecmd.c. Prints program usage message and
+	terminates with the given exit status.
+*/
 void usage(int status) NORETURN;
 
+/*
+	To implement a new command, add a global, static instance of a
+	command_t (or derived) structure to a C file and pass it to this
+	macro to have it automatically registered on program startup.
+*/
 #define REGISTER_COMMAND(cmd) \
 	static void __attribute__((constructor)) register_##cmd(void) \
 	{ \