size Command Linux: Display Section Sizes of Object Files and Executables

The size command is a powerful utility in Linux systems that displays the section sizes of object files, executables, and libraries. This essential tool helps developers and system administrators analyze memory usage, optimize code, and understand how programs utilize system resources.

What is the size Command?

The size command reads one or more object files and displays the sizes of their various sections. It’s particularly useful for examining compiled programs, shared libraries, and object files to understand their memory footprint and structure.

Basic Syntax

size [options] [file...]

Understanding ELF File Sections

Before diving into examples, it’s important to understand the main sections that the size command analyzes:

• text: Contains the executable code
• data: Contains initialized global and static variables
• bss: Contains uninitialized global and static variables

Basic Usage Examples

Analyzing a Simple Executable

Let’s start with examining a basic executable:

$ size /usr/bin/ls

Output:

   text    data     bss     dec     hex filename
 133251    4864    4616  142731   22d7b /usr/bin/ls

This output shows:

• text: 133,251 bytes of executable code
• data: 4,864 bytes of initialized data
• bss: 4,616 bytes of uninitialized data
• dec: 142,731 total bytes in decimal
• hex: 22d7b total bytes in hexadecimal

Examining Multiple Files

$ size /usr/bin/cat /usr/bin/grep /usr/bin/find

Output:

   text    data     bss     dec     hex filename
  27891    1328     288   29507    7363 /usr/bin/cat
 183107    3152    1024  187283   25bd3 /usr/bin/grep
 284738    5456    2368  292562   476f2 /usr/bin/find

Command Options and Flags

Berkeley Format (-B or –format=berkeley)

This is the default format, showing text, data, and bss sections:

$ size -B /usr/bin/vim

Output:

   text    data     bss     dec     hex filename
2847147   83600   44800 2975547  2d6e2b /usr/bin/vim

SysV Format (-A or –format=sysv)

This format provides detailed information about all sections:

$ size -A /usr/bin/cat

Output:

/usr/bin/cat  :
section               size      addr
.interp                 28   0x400238
.note.ABI-tag           32   0x400254
.note.gnu.build-id      36   0x400274
.gnu.hash               60   0x400298
.dynsym                768   0x4002d0
.dynstr                394   0x4005d0
.gnu.version            64   0x40075a
.gnu.version_r          80   0x40079c
.rela.dyn              192   0x4007ec
.rela.plt              456   0x4008ac
.init                   26   0x400a78
.plt                   320   0x400a90
.text                25893   0x400bb0
.fini                    9   0x4071c5
.rodata                1694   0x4071d0
.eh_frame_hdr           156   0x407840
.eh_frame               588   0x4078dc
.init_array               8   0x608b00
.fini_array               8   0x608b08
.dynamic                464   0x608b10
.got                      8   0x608ce0
.got.plt                168   0x608ce8
.data                   272   0x608d90
.bss                    288   0x608ea0
Total                 29507

Radix Options

Display sizes in different number bases:

# Octal format
$ size -o /usr/bin/cat

Output:

   text    data     bss     oct     hex filename
  27891    1328     288   71603    7363 /usr/bin/cat

# Hexadecimal format
$ size -x /usr/bin/cat

Output:

   text    data     bss     dec     hex filename
   6cf3     530     120    7363    7363 /usr/bin/cat

Decimal Format (-d)

$ size -d /usr/bin/cat

Output:

   text    data     bss     dec     hex filename
  27891    1328     288   29507    7363 /usr/bin/cat

Advanced Usage Scenarios

Analyzing Shared Libraries

$ size /lib/x86_64-linux-gnu/libc.so.6

Output:

   text    data     bss     dec     hex filename
1824143   45312   13624 1883079  1cc0b7 /lib/x86_64-linux-gnu/libc.so.6

Examining Object Files

When working with compiled object files:

$ gcc -c hello.c
$ size hello.o

Output:

   text    data     bss     dec     hex filename
     89       0       0      89      59 hello.o

Sorting Output

While the size command doesn’t have built-in sorting, you can combine it with other tools:

$ size /usr/bin/* | sort -k4 -n | tail -5

This sorts files by total size (decimal column) and shows the largest 5:

   text    data     bss     dec     hex filename
1247299   49136    7936 1304371  13e5d3 /usr/bin/python3.9
1824143   45312   13624 1883079  1cc0b7 /usr/bin/dpkg
2463747   63584    8320 2535651  26b7e3 /usr/bin/git
2847147   83600   44800 2975547  2d6e2b /usr/bin/vim
4521299  183648   36096 4741043  485d53 /usr/bin/gcc

Practical Applications

Code Optimization

Use size to monitor how code changes affect memory usage:

# Before optimization
$ size myprogram
   text    data     bss     dec     hex filename
  45678    2340    1024   49042    bf92 myprogram

# After optimization
$ size myprogram
   text    data     bss     dec     hex filename
  42156    2340    1024   45520    b1f0 myprogram

Library Comparison

Compare different versions or implementations:

$ size /usr/lib/x86_64-linux-gnu/libssl.so.1.1 /usr/lib/x86_64-linux-gnu/libssl.so.3

Embedded Development

For embedded systems with memory constraints:

$ size firmware.elf
   text    data     bss     dec     hex filename
  32768    1024    4096   37888    9400 firmware.elf

Integration with Build Systems

Using with Make

Add size analysis to your Makefile:

analyze: $(TARGET)
	@echo "Memory usage analysis:"
	@size $(TARGET)
	@echo "Text section uses $$(size $(TARGET) | tail -1 | awk '{print $$1}') bytes"

Continuous Integration

Monitor binary size in CI/CD pipelines:

#!/bin/bash
MAX_SIZE=1048576  # 1MB limit
CURRENT_SIZE=$(size myapp | tail -1 | awk '{print $4}')

if [ $CURRENT_SIZE -gt $MAX_SIZE ]; then
    echo "Error: Binary size ($CURRENT_SIZE) exceeds limit ($MAX_SIZE)"
    exit 1
fi

Troubleshooting Common Issues

File Not Found Errors

$ size nonexistent
size: nonexistent: No such file

Invalid File Format

$ size textfile.txt
size: textfile.txt: file format not recognized

Permission Issues

$ size /restricted/file
size: /restricted/file: Permission denied

Best Practices

1. Regular Monitoring: Include size analysis in your development workflow
2. Version Tracking: Compare sizes across different versions of your software
3. Memory Planning: Use size information for embedded system memory allocation
4. Optimization Validation: Verify that code optimizations actually reduce binary size

Related Commands

• nm: List symbols in object files
• objdump: Display information about object files
• readelf: Display information about ELF files
• strip: Remove symbols from object files

Conclusion

The size command is an invaluable tool for developers and system administrators working with compiled code. Whether you’re optimizing applications for embedded systems, monitoring memory usage in large applications, or simply understanding how your code translates to binary format, mastering the size command will enhance your development and analysis capabilities.

By incorporating size analysis into your development workflow, you can make informed decisions about code optimization, memory allocation, and system resource planning. The command’s simplicity belies its power in providing crucial insights into your programs’ memory footprint.