# Install required software
sudo apt-get install build-essential autoconf libtool liblzma-dev libglib2.0-dev git  # for Ubuntu
## sudo yum install gcc make autoconf libtool xz-devel glib2-devel git  # for CentOS
  
# Compile utilities and install
git clone https://github.com/rssnsj/firmware-tools.git firmware-tools
cd firmware-tools
make
make install

 openwrt-repack.sh <ROM_file> [options] ...    patch firmware <ROM_file> and repackage
 openwrt-repack.sh -c                          clean temporary and target files
 
Options:
 -o <output_file>          filename of newly built firmware
 -r <package>              remove opkg package (can be multiple)
 -i <package>              install package with ipk file path or URL (can be multiple)
 -e                        enable root login
 -w                        enable wireless by default
 -x <commands>             execute commands after all other operations

rssnsj@precise-vmx:~/roms$ openwrt-repack.sh openwrt-ramips-mt7620a-hiwifi-hc5761-squashfs-sysupgrade.bin -w -e -i tcpdump
>>> Analysing source firmware: openwrt-ramips-mt7620a-hiwifi-hc5761-squashfs-sysupgrade.bin ...
Found SquashFS at 1077084.
>>> Extracting kernel, rootfs partitions ...
>>> Extracting SquashFS into directory squashfs-root/ ...
Parallel unsquashfs: Using 4 processors
1488 inodes (1502 blocks) to write
  
[===============================================================================================|] 1502/1502 100%
created 1259 files
created 104 directories
created 228 symlinks
created 0 devices
created 0 fifos
>>> Patching the firmware ...
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ramips/mt7620a/packages/base/Packages.gz.
Inflating http://downloads.openwrt.org/barrier_breaker/14.07/ramips/mt7620a/packages/base/Packages.gz.
... ...
Installing tcpdump (4.5.1-4) to root...
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ramips/mt7620a/packages/base/tcpdump_4.5.1-4_ramips_24kec.ipk.
Installing libpcap (1.5.3-1) to root...
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ramips/mt7620a/packages/base/libpcap_1.5.3-1_ramips_24kec.ipk.
Configuring libpcap.
Configuring tcpdump.
Checking init.d scripts for newly installed services ...
>>> Repackaging the modified firmware ...
Parallel mksquashfs: Using 1 processor
Creating 4.0 filesystem on root.squashfs, block size 262144.
Pseudo file "/dev" exists in source filesystem "/home/rssnsj/roms/squashfs-root/dev".
Ignoring, exclude it (-e/-ef) to override.
[===============================================================================================|] 1281/1281 100%
Exportable Squashfs 4.0 filesystem, xz compressed, data block size 262144
        compressed data, compressed metadata, compressed fragments, compressed xattrs
... ...
Directory table size 15678 bytes (15.31 Kbytes)
        46.62% of uncompressed directory table size (33629 bytes)
Number of duplicate files found 9
... ...
padding image to 006b0000
padding image to 006c0000
>>> Done. New firmware: openwrt-ramips-mt7620a-hiwifi-hc5761-squashfs-sysupgrade.bin.out
rssnsj@precise-vmx:~/roms$