[build]: Move Systemd service start to systemd generator (#3172)

- What I did

 Move the enabling of Systemd services from sonic_debian_extension to a new systemd generator

- How I did it

  Create a new systemd generator to manually create symlinks to enable systemd services
  Add rules/Makefile to build generator
  Add services to be enabled to /etc/sonic/generated_services.conf to be read by the generator at boot time

Signed-off-by: Lawrence Lee <t-lale@microsoft.com>

.gitignore

@@ -81,6 +81,12 @@ src/supervisor/*
 !src/supervisor/patch/
 src/swig/*
 !src/swig/Makefile
+src/systemd-sonic-generator/systemd-sonic-generator
+src/systemd-sonic-generator/debian/*
+!src/systemd-sonic-generator/debian/changelog
+!src/systemd-sonic-generator/debian/compat
+!src/systemd-sonic-generator/debian/control
+!src/systemd-sonic-generator/debian/rules
 src/telemetry/debian/*
 !src/telemetry/debian/changelog
 !src/telemetry/debian/compat

files/build_templates/sonic_debian_extension.j2

@@ -37,6 +37,8 @@ FILESYSTEM_ROOT_USR_SHARE="$FILESYSTEM_ROOT_USR/share"
 FILESYSTEM_ROOT_USR_SHARE_SONIC="$FILESYSTEM_ROOT_USR_SHARE/sonic"
 FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES="$FILESYSTEM_ROOT_USR_SHARE_SONIC/templates"
 
+GENERATED_SERVICE_FILE="$FILESYSTEM_ROOT/etc/sonic/generated_services.conf"
+
 clean_sys() {
     sudo umount $FILESYSTEM_ROOT/sys/fs/cgroup/*            \
                 $FILESYSTEM_ROOT/sys/fs/cgroup              \
@@ -157,21 +159,21 @@ sudo cp -f $IMAGE_CONFIGS/cron.d/* $FILESYSTEM_ROOT/etc/cron.d/
 
 # Copy NTP configuration files and templates
 sudo cp $IMAGE_CONFIGS/ntp/ntp-config.service $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable ntp-config.service
+echo "ntp-config.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/ntp/ntp-config.sh $FILESYSTEM_ROOT/usr/bin/
 sudo cp $IMAGE_CONFIGS/ntp/ntp.conf.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES/
 
 # Copy warmboot-finalizer files
 sudo LANG=C cp $IMAGE_CONFIGS/warmboot-finalizer/finalize-warmboot.sh $FILESYSTEM_ROOT/usr/local/bin/finalize-warmboot.sh
 sudo LANG=C cp $IMAGE_CONFIGS/warmboot-finalizer/warmboot-finalizer.service $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable warmboot-finalizer.service
+echo "warmboot-finalizer.service" | sudo tee -a $GENERATED_SERVICE_FILE
 
 # Copy rsyslog configuration files and templates
 sudo cp $IMAGE_CONFIGS/rsyslog/rsyslog-config.service  $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable rsyslog-config.service
 sudo cp $IMAGE_CONFIGS/rsyslog/rsyslog-config.sh $FILESYSTEM_ROOT/usr/bin/
 sudo cp $IMAGE_CONFIGS/rsyslog/rsyslog.conf.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES/
 sudo cp $IMAGE_CONFIGS/rsyslog/rsyslog.d/* $FILESYSTEM_ROOT/etc/rsyslog.d/
+echo "rsyslog-config.service" | sudo tee -a $GENERATED_SERVICE_FILE
 
 # Copy logrotate.d configuration files
 sudo cp -f $IMAGE_CONFIGS/logrotate/logrotate.d/* $FILESYSTEM_ROOT/etc/logrotate.d/
@@ -181,9 +183,9 @@ sudo cp -f $IMAGE_CONFIGS/systemd/journald.conf $FILESYSTEM_ROOT/etc/systemd/
 
 # Copy interfaces configuration files and templates
 sudo cp $IMAGE_CONFIGS/interfaces/interfaces-config.service  $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable interfaces-config.service
 sudo cp $IMAGE_CONFIGS/interfaces/interfaces-config.sh $FILESYSTEM_ROOT/usr/bin/
 sudo cp $IMAGE_CONFIGS/interfaces/*.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES/
+echo "interfaces-config.service" | sudo tee -a $GENERATED_SERVICE_FILE
 
 # Copy initial interfaces configuration file, will be overwritten on first boot
 sudo cp $IMAGE_CONFIGS/interfaces/init_interfaces $FILESYSTEM_ROOT/etc/network/interfaces
@@ -191,7 +193,7 @@ sudo mkdir -p $FILESYSTEM_ROOT/etc/network/interfaces.d
 
 # Copy hostcfgd files
 sudo cp $IMAGE_CONFIGS/hostcfgd/hostcfgd.service $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable hostcfgd.service
+echo "hostcfgd.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/hostcfgd/hostcfgd $FILESYSTEM_ROOT/usr/bin/
 sudo cp $IMAGE_CONFIGS/hostcfgd/*.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES/
 
@@ -203,13 +205,13 @@ sudo cp $BUILD_TEMPLATES/qos_config.j2 $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATE
 
 # Copy hostname configuration scripts
 sudo cp $IMAGE_CONFIGS/hostname/hostname-config.service  $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable hostname-config.service
+echo "hostname-config.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/hostname/hostname-config.sh $FILESYSTEM_ROOT/usr/bin/
 
 # Copy updategraph script and service file
 j2 files/build_templates/updategraph.service.j2 | sudo tee $FILESYSTEM_ROOT/etc/systemd/system/updategraph.service
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable updategraph.service
 sudo cp $IMAGE_CONFIGS/updategraph/updategraph $FILESYSTEM_ROOT/usr/bin/
+echo "updategraph.service" | sudo tee -a $GENERATED_SERVICE_FILE
 {% if enable_dhcp_graph_service == "y" %}
 sudo bash -c "echo enabled=true > $FILESYSTEM_ROOT/etc/sonic/updategraph.conf"
 sudo bash -c "echo src=dhcp >> $FILESYSTEM_ROOT/etc/sonic/updategraph.conf"
@@ -235,12 +237,12 @@ sudo cp $IMAGE_CONFIGS/sudoers/sudoers.lecture $FILESYSTEM_ROOT/etc/
 
 # Copy control plane ACL management daemon files
 sudo cp $IMAGE_CONFIGS/caclmgrd/caclmgrd.service  $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable caclmgrd.service
+echo "caclmgrd.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/caclmgrd/caclmgrd $FILESYSTEM_ROOT/usr/bin/
 
 # Copy process-reboot-cause service files
 sudo cp $IMAGE_CONFIGS/process-reboot-cause/process-reboot-cause.service  $FILESYSTEM_ROOT/etc/systemd/system/
-sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable process-reboot-cause.service
+echo "process-reboot-cause.service" | sudo tee -a $GENERATED_SERVICE_FILE
 sudo cp $IMAGE_CONFIGS/process-reboot-cause/process-reboot-cause $FILESYSTEM_ROOT/usr/bin/
 
 ## Install package without starting service
@@ -331,7 +333,7 @@ sudo cp {{script}} $FILESYSTEM_ROOT/usr/bin/
 {% for service in installer_services.split(' ') -%}
 if [ -f {{service}} ]; then
     sudo cp {{service}} $FILESYSTEM_ROOT/etc/systemd/system/
-    sudo LANG=C chroot $FILESYSTEM_ROOT systemctl enable {{service}}
+    echo "{{service}}" | sudo tee -a $GENERATED_SERVICE_FILE
 fi
 {% endfor %}
 sudo LANG=C chroot $FILESYSTEM_ROOT fuser -km /sys || true

platform/barefoot/one-aboot.mk

@@ -4,6 +4,7 @@ SONIC_ONE_ABOOT_IMAGE = sonic-aboot-barefoot.swi
 $(SONIC_ONE_ABOOT_IMAGE)_MACHINE = barefoot
 $(SONIC_ONE_ABOOT_IMAGE)_IMAGE_TYPE = aboot
 $(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(BFN_MODULE)
+$(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_ABOOT_IMAGE)_LAZY_INSTALLS += $(BFN_PLATFORM_MODULE)
 $(SONIC_ONE_ABOOT_IMAGE)_LAZY_INSTALLS += $(BFN_MONTARA_PLATFORM_MODULE)
 $(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(ARISTA_PLATFORM_MODULE_DRIVERS) \

platform/barefoot/one-image.mk

@@ -4,6 +4,7 @@ SONIC_ONE_IMAGE = sonic-barefoot.bin
 $(SONIC_ONE_IMAGE)_MACHINE = barefoot
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 $(SONIC_ONE_IMAGE)_INSTALLS += $(BFN_MODULE) $(PYTHON_THRIFT)
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(BFN_PLATFORM_MODULE)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(BFN_MONTARA_PLATFORM_MODULE)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(WNC_OSW1800_PLATFORM_MODULE) 

platform/broadcom/one-aboot.mk

@@ -4,5 +4,6 @@ SONIC_ONE_ABOOT_IMAGE = sonic-aboot-broadcom.swi
 $(SONIC_ONE_ABOOT_IMAGE)_MACHINE = broadcom
 $(SONIC_ONE_ABOOT_IMAGE)_IMAGE_TYPE = aboot
 $(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(BRCM_OPENNSL_KERNEL) $(ARISTA_PLATFORM_MODULE_DRIVERS) $(ARISTA_PLATFORM_MODULE_PYTHON2) $(ARISTA_PLATFORM_MODULE_PYTHON3) $(ARISTA_PLATFORM_MODULE)
+$(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_ABOOT_IMAGE)_DOCKERS += $(SONIC_INSTALL_DOCKER_IMAGES)
 SONIC_INSTALLERS += $(SONIC_ONE_ABOOT_IMAGE)

platform/broadcom/one-image.mk

@@ -4,6 +4,7 @@ SONIC_ONE_IMAGE = sonic-broadcom.bin
 $(SONIC_ONE_IMAGE)_MACHINE = broadcom
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 $(SONIC_ONE_IMAGE)_INSTALLS += $(BRCM_OPENNSL_KERNEL)
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(DELL_S6000_PLATFORM_MODULE) \
                                $(DELL_Z9264F_PLATFORM_MODULE) \
                                $(DELL_S5232F_PLATFORM_MODULE) \

platform/broadcom/raw-image.mk

@@ -4,6 +4,7 @@ SONIC_RAW_IMAGE = sonic-broadcom.raw
 $(SONIC_RAW_IMAGE)_MACHINE = broadcom
 $(SONIC_RAW_IMAGE)_IMAGE_TYPE = raw
 $(SONIC_RAW_IMAGE)_INSTALLS += $(BRCM_OPENNSL_KERNEL)
+$(SONIC_RAW_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_RAW_IMAGE)_LAZY_INSTALLS += $($(SONIC_ONE_IMAGE)_LAZY_INSTALLS)
 $(SONIC_RAW_IMAGE)_DOCKERS += $(SONIC_INSTALL_DOCKER_IMAGES)
 SONIC_INSTALLERS += $(SONIC_RAW_IMAGE)

platform/cavium/one-image.mk

@@ -5,6 +5,7 @@ $(SONIC_ONE_IMAGE)_MACHINE = cavium
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 $(SONIC_ONE_IMAGE)_INSTALLS += $(CAVM_PLATFORM_DEB)
 $(SONIC_ONE_IMAGE)_INSTALLS += $(CAVM_XPNET_DEB)
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 ifeq ($(INSTALL_DEBUG_TOOLS),y)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(SONIC_INSTALL_DOCKER_DBG_IMAGES)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(filter-out $(patsubst %-$(DBG_IMAGE_MARK).gz,%.gz, $(SONIC_INSTALL_DOCKER_DBG_IMAGES)), $(SONIC_INSTALL_DOCKER_IMAGES))

platform/centec/one-image.mk

@@ -3,6 +3,7 @@
 SONIC_ONE_IMAGE = sonic-centec.bin
 $(SONIC_ONE_IMAGE)_MACHINE = centec
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
+$(SONIC_ONE_IMAGE)_INSTALLS = $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(CENTEC_E582_48X6Q_PLATFORM_MODULE) \
                                     $(CENTEC_E582_48X2Q4Z_PLATFORM_MODULE)
 ifeq ($(INSTALL_DEBUG_TOOLS),y)

platform/generic/aboot-image.mk

@@ -3,6 +3,6 @@
 SONIC_GENERIC_ABOOT_IMAGE = sonic-aboot-generic.swi
 $(SONIC_GENERIC_ABOOT_IMAGE)_MACHINE = generic
 $(SONIC_GENERIC_ABOOT_IMAGE)_IMAGE_TYPE = aboot
-$(SONIC_GENERIC_ABOOT_IMAGE)_INSTALLS =
+$(SONIC_GENERIC_ABOOT_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_GENERIC_ABOOT_IMAGE)_DOCKERS =
 SONIC_INSTALLERS += $(SONIC_GENERIC_ABOOT_IMAGE)

platform/generic/onie-image.mk

@@ -3,6 +3,6 @@
 SONIC_GENERIC_ONIE_IMAGE = sonic-generic.bin
 $(SONIC_GENERIC_ONIE_IMAGE)_MACHINE = generic
 $(SONIC_GENERIC_ONIE_IMAGE)_IMAGE_TYPE = onie
-$(SONIC_GENERIC_ONIE_IMAGE)_INSTALLS =
+$(SONIC_GENERIC_ONIE_IMAGE)_INSTALLS = $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_GENERIC_ONIE_IMAGE)_DOCKERS =
 SONIC_INSTALLERS += $(SONIC_GENERIC_ONIE_IMAGE)

platform/marvell/one-image.mk

@@ -3,6 +3,7 @@
 SONIC_ONE_IMAGE = sonic-marvell.bin
 $(SONIC_ONE_IMAGE)_MACHINE = marvell
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 ifeq ($(INSTALL_DEBUG_TOOLS),y)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(SONIC_INSTALL_DOCKER_DBG_IMAGES)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(filter-out $(patsubst %-$(DBG_IMAGE_MARK).gz,%.gz, $(SONIC_INSTALL_DOCKER_DBG_IMAGES)), $(SONIC_INSTALL_DOCKER_IMAGES))

platform/mellanox/one-image.mk

@@ -4,6 +4,7 @@ SONIC_ONE_IMAGE = sonic-mellanox.bin
 $(SONIC_ONE_IMAGE)_MACHINE = mellanox
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 $(SONIC_ONE_IMAGE)_INSTALLS += $(SX_KERNEL) $(KERNEL_MFT) $(MFT_OEM) $(MFT) $(MLNX_HW_MANAGEMENT)
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 ifeq ($(INSTALL_DEBUG_TOOLS),y)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(SONIC_INSTALL_DOCKER_DBG_IMAGES)
 $(SONIC_ONE_IMAGE)_DOCKERS += $(filter-out $(patsubst %-$(DBG_IMAGE_MARK).gz,%.gz, $(SONIC_INSTALL_DOCKER_DBG_IMAGES)), $(SONIC_INSTALL_DOCKER_IMAGES))

platform/nephos/one-image.mk

@@ -4,6 +4,7 @@ SONIC_ONE_IMAGE = sonic-nephos.bin
 $(SONIC_ONE_IMAGE)_MACHINE = nephos
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 $(SONIC_ONE_IMAGE)_INSTALLS += $(NEPHOS_MODULE)
+$(SONIC_ONE_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_IMAGE)_LAZY_INSTALLS += $(INGRASYS_S9130_32X_PLATFORM_MODULE) \
                                $(INGRASYS_S9230_64X_PLATFORM_MODULE) \
                                $(ACCTON_AS7116_54X_PLATFORM_MODULE)  \

platform/vs/kvm-image.mk

@@ -1,6 +1,7 @@
 # sonic kvm image
 
 SONIC_KVM_IMAGE = sonic-vs.img.gz
+$(SONIC_KVM_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_KVM_IMAGE)_MACHINE = vs
 $(SONIC_KVM_IMAGE)_IMAGE_TYPE = kvm
 ifeq ($(INSTALL_DEBUG_TOOLS),y)

platform/vs/one-image.mk

@@ -1,6 +1,7 @@
 # sonic vs one image installer
 
 SONIC_ONE_IMAGE = sonic-vs.bin
+$(SONIC_ONE_ABOOT_IMAGE)_INSTALLS += $(SYSTEMD_SONIC_GENERATOR)
 $(SONIC_ONE_IMAGE)_MACHINE = vs
 $(SONIC_ONE_IMAGE)_IMAGE_TYPE = onie
 ifeq ($(INSTALL_DEBUG_TOOLS),y)

rules/systemd-sonic-generator.mk

@@ -0,0 +1,3 @@
+SYSTEMD_SONIC_GENERATOR = systemd-sonic-generator_1.0.0_$(CONFIGURED_ARCH).deb
+$(SYSTEMD_SONIC_GENERATOR)_SRC_PATH = $(SRC_PATH)/systemd-sonic-generator
+SONIC_MAKE_DEBS += $(SYSTEMD_SONIC_GENERATOR)

src/systemd-sonic-generator/Makefile

@@ -0,0 +1,22 @@
+CC=gcc
+CFLAGS=-std=gnu99
+
+BINARY = systemd-sonic-generator
+MAIN_TARGET = $(BINARY)_1.0.0_$(CONFIGURED_ARCH).deb
+
+$(addprefix $(DEST)/, $(MAIN_TARGET)): $(DEST)/% :
+	dpkg-buildpackage -us -uc -b
+	mv ../$(MAIN_TARGET) $(DEST)/
+	rm ../$(BINARY)-* ../$(BINARY)_*
+
+$(BINARY): systemd-sonic-generator.c
+	rm -f ./systemd-sonic-generator
+
+	$(CC) $(CFLAGS) -o $@ $^
+
+install: $(BINARY)
+	mkdir -p $(DESTDIR)
+	mkdir -p $(DESTDIR)/lib
+	mkdir -p $(DESTDIR)/lib/systemd
+	mkdir -p $(DESTDIR)/lib/systemd/system-generators
+	cp ./systemd-sonic-generator $(DESTDIR)/lib/systemd/system-generators

src/systemd-sonic-generator/debian/changelog

@@ -0,0 +1,3 @@
+systemd-sonic-generator (1.0.0) UNRELEASED; urgency=medium
+    * Initial version
+    -- Lawrence Lee <t-lale@microsoft.com> Tue, 23 Jul 2019 16:00:00 -0800

src/systemd-sonic-generator/debian/compat

@@ -0,0 +1 @@
+11

src/systemd-sonic-generator/debian/control

@@ -0,0 +1,6 @@
+Source: systemd-sonic-generator
+Maintainer: Lawrence Lee <t-lale@microsoft.com>
+
+Package: systemd-sonic-generator
+Architecture: any
+Description: Systemd generator for SONiC services

src/systemd-sonic-generator/debian/rules

@@ -0,0 +1,18 @@
+#!/usr/bin/make -f
+
+DISTRIBUTION = $(shell sed -n "s/^VERSION_CODENAME=//p" /etc/os-release)
+VERSION = 1.0.0
+PACKAGEVERSION = $(VERSION)
+
+%:
+	dh $@
+
+override_dh_auto_clean:
+override_dh_auto_test:
+override_dh_auto_build:
+override_dh_auto_install:
+	make systemd-sonic-generator
+	make install DESTDIR=debian/systemd-sonic-generator
+
+override_dh_gencontrol:
+	dh_gencontrol -- -v$(PACKAGEVERSION)

src/systemd-sonic-generator/systemd-sonic-generator.c

@@ -0,0 +1,309 @@
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <linux/limits.h>
+
+#define MAX_NUM_TARGETS 5
+#define MAX_NUM_INSTALL_LINES 5
+#define MAX_NUM_UNITS 128
+
+static const char* UNIT_FILE_PREFIX = "/etc/systemd/system/";
+static const char* CONFIG_FILE = "/etc/sonic/generated_services.conf";
+
+
+void strip_trailing_newline(char* str) {
+    /***
+    Strips trailing newline from a string if it exists
+    ***/
+
+    size_t l = strlen(str);
+    if (l > 0 && str[l-1] == '\n')
+        str[l-1] = '\0';
+}
+
+
+static int get_target_lines(char* unit_file, char* target_lines[]) {
+    /***
+    Gets installation information for a given unit file
+
+    Returns lines in the [Install] section of a unit file
+    ***/
+    FILE *fp;
+    char *line = NULL;
+    size_t len = 0;
+    ssize_t nread;
+    bool found_install;
+    int num_target_lines;
+
+
+    fp = fopen(unit_file, "r");
+
+    if (fp == NULL) {
+        fprintf(stderr, "Failed to open file %s\n", unit_file);
+        return -1;
+    }
+
+    found_install = false;
+    num_target_lines = 0;
+
+    while ((nread = getline(&line, &len, fp)) != -1 ) {
+        // Assumes that [Install] is the last section of the unit file
+        if (strstr(line, "[Install]") != NULL) {
+             found_install = true;
+        }
+        else if (found_install) {
+            if (num_target_lines >= MAX_NUM_INSTALL_LINES) {
+                fprintf(stderr, "Number of lines in [Install] section of %s exceeds MAX_NUM_INSTALL_LINES\n", unit_file);
+                fputs("Extra [Install] lines will be ignored\n", stderr);
+                return num_target_lines;
+            }
+            target_lines[num_target_lines] = strdup(line);
+            num_target_lines++;
+        }
+    }
+
+    free(line);
+
+    fclose(fp);
+
+    return num_target_lines;
+}
+
+static int get_install_targets_from_line(char* target_string, char* suffix, char* targets[], int existing_targets) {
+    /***
+    Helper fuction for get_install_targets
+
+    Given a space delimited string of target directories and a suffix,
+    puts each target directory plus the suffix into the targets array
+    ***/
+    char* token;
+    char* target;
+    char final_target[PATH_MAX];
+    int num_targets = 0;
+
+    while ((token = strtok_r(target_string, " ", &target_string))) {
+        target = strdup(token);
+        strip_trailing_newline(target);
+
+        strcpy(final_target, target);
+        strcat(final_target, suffix);
+
+        free(target);
+
+        if (num_targets + existing_targets >= MAX_NUM_TARGETS) {
+            fputs("Number of targets found exceeds MAX_NUM_TARGETS\n", stderr);
+            fputs("Additional targets will be ignored \n", stderr);
+            return num_targets;
+        }
+
+        targets[num_targets + existing_targets] = strdup(final_target);
+        num_targets++;
+    }
+    return num_targets;
+}
+
+static int get_install_targets(char* unit_file, char* targets[]) {
+    /***
+    Returns install targets for a unit file
+
+    Parses the information in the [Install] section of a given
+    unit file to determine which directories to install the unit in
+    ***/
+    char file_path[PATH_MAX];
+    char *target_lines[MAX_NUM_INSTALL_LINES];
+    int num_target_lines;
+    int num_targets;
+    int found_targets;
+    char* token;
+    char* line = NULL;
+    bool first;
+    char* target_suffix;
+
+    strcpy(file_path, UNIT_FILE_PREFIX);
+    strcat(file_path, unit_file);
+
+    num_target_lines = get_target_lines(file_path, target_lines);
+    if (num_target_lines < 0) {
+        fprintf(stderr, "Error parsing targets for %s\n", unit_file);
+        return -1;
+    }
+
+    num_targets = 0;
+
+    for (int i = 0; i < num_target_lines; i++) {
+        line = target_lines[i];
+        first = true;
+
+        while ((token = strtok_r(line, "=", &line))) {
+            if (first) {
+                first = false;
+
+                if (strstr(token, "RequiredBy") != NULL) {
+                    target_suffix = ".requires";
+                }
+                else if (strstr(token, "WantedBy") != NULL) {
+                    target_suffix = ".wants";
+                }
+            }
+            else {
+                found_targets = get_install_targets_from_line(token, target_suffix, targets, num_targets);
+                num_targets += found_targets;
+            }
+        }
+        free(target_lines[i]);
+    }
+    return num_targets;
+}
+
+
+static int get_unit_files(char* unit_files[]) {
+    /***
+    Reads a list of unit files to be installed from /etc/sonic/generated_services.conf
+    ***/
+    FILE *fp;
+    char *line = NULL;
+    size_t len = 0;
+    ssize_t read;
+
+    fp = fopen(CONFIG_FILE, "r");
+
+    if (fp == NULL) {
+        fprintf(stderr, "Failed to open %s\n", CONFIG_FILE);
+        exit(EXIT_FAILURE);
+    }
+
+    int num_unit_files = 0;
+
+    while ((read = getline(&line, &len, fp)) != -1) {
+        if (num_unit_files >= MAX_NUM_UNITS) {
+            fprintf(stderr, "Maximum number of units exceeded, ignoring extras\n");
+            return num_unit_files;
+        }
+        strip_trailing_newline(line);
+        unit_files[num_unit_files] = strdup(line);
+        num_unit_files++;
+    }
+
+    free(line);
+
+    fclose(fp);
+
+    return num_unit_files;
+}
+
+
+static int install_unit_file(char* unit_file, char* target, char* install_dir) {
+    /***
+    Creates a symlink for a unit file installation
+
+    For a given unit file and target directory,
+    create the appropriate symlink in the target directory
+    to enable the unit and have it started by Systemd
+    ***/
+    char final_install_dir[PATH_MAX];
+    char src_path[PATH_MAX];
+    char dest_path[PATH_MAX];
+    struct stat st;
+    int r;
+
+    assert(unit_file);
+    assert(target);
+
+    strcpy(final_install_dir, install_dir);
+    strcat(final_install_dir, target);
+
+    strcpy(src_path, UNIT_FILE_PREFIX);
+    strcat(src_path, unit_file);
+
+    if (stat(final_install_dir, &st) == -1) {
+        // If doesn't exist, create
+        r = mkdir(final_install_dir, 0755);
+        if (r == -1) {
+            fprintf(stderr, "Unable to create target directory %s\n", final_install_dir);
+            return -1;
+        }
+    }
+    else if (S_ISREG(st.st_mode)) {
+        // If is regular file, remove and create
+        r = remove(final_install_dir);
+        if (r == -1) {
+            fprintf(stderr, "Unable to remove file with same name as target directory %s\n", final_install_dir);
+            return -1;
+        }
+
+        r = mkdir(final_install_dir, 0755);
+        if (r == -1) {
+            fprintf(stderr, "Unable to create target directory %s\n", final_install_dir);
+            return -1;
+        }
+    }  
+    else if (S_ISDIR(st.st_mode)) {
+        // If directory, verify correct permissions
+        r = chmod(final_install_dir, 0755);
+        if (r == -1) {
+            fprintf(stderr, "Unable to change permissions of existing target directory %s\n", final_install_dir);
+            return -1;
+        }
+    }
+        
+
+    strcpy(dest_path, final_install_dir);
+    strcat(dest_path, "/");
+    strcat(dest_path, unit_file);
+
+    r = symlink(src_path, dest_path);
+
+    if (r < 0) {
+        if (errno == EEXIST)
+            return 0;
+        fprintf(stderr, "Error creating symlink %s from source %s\n", dest_path, src_path);
+        return -1;
+    }
+
+    return 0;
+}
+
+
+int main(int argc, char **argv) {
+    char* unit_files[MAX_NUM_UNITS];
+    char install_dir[PATH_MAX];
+    char* targets[MAX_NUM_TARGETS];
+    int num_unit_files;
+    int num_targets;
+
+    if (argc <= 1) {
+        fputs("Installation directory required as argument\n", stderr);
+        return 1;
+    }
+
+    strcpy(install_dir, argv[1]);
+    strcat(install_dir, "/");
+
+    num_unit_files = get_unit_files(unit_files);
+
+    // For each unit file, get the installation targets and install the unit
+    for (int i = 0; i < num_unit_files; i++) {
+        num_targets = get_install_targets(unit_files[i], targets);
+        if (num_targets < 0) {
+            fprintf(stderr, "Error parsing %s\n", unit_files[i]);
+            free(unit_files[i]);
+            continue;
+        }
+
+        for (int j = 0; j < num_targets; j++) {
+            if (install_unit_file(unit_files[i], targets[j], install_dir) != 0)
+                fprintf(stderr, "Error installing %s to target directory %s\n", unit_files[i], targets[j]);
+
+            free(targets[j]);
+        }
+
+        free(unit_files[i]);
+    }
+    return 0;
+}