Can't execute .out files, getting permission denied

I have written a C++ program and complied it to produce a.out file. However, whenever I try to run it, I get Permission Denied. I read that we can use sudo, but I can't quite get it to work. I use something like, sudo "./a.out" but that too doesn't work.

Edit:

Here is the message I get when I try "./a.out".

bash: ./a.out: Permission denied

Solution 1:

Usually, g++ gives the created file execute permissions. If you do not pass the -o option, the file will be named a.out.

Two possible reasons why your file does not have the execute bit set, with their solutions:

1. The umask value is set to a value like 0133, thereby preventing the execute bit from being set. Solution: set the permissions explicitly:

   chmod 755 a.out
   

2. The filesystem you're working on does not support Linux permissions. This could be the case if you're putting files on a FAT32-formatted flash drive. Solution: either back up the files and format it to ext2 or mount the drive with fmask=0022 or umask=0022 (omitting fmask). See the Mount options for fat section on the manual page of mount for more details.

For bash scripts which do not have the execute bit set, you could run bash file.sh. Such a feature exists for all files with executable content (compiled files and files with a shebang line #!/path/to/interpreter set). To execute files without the execute bit set, use the special file /lib/ld-linux.so.2 (or /lib/ld-linux-x86-64.so.2 for 64-bit applications) to run such a program:

/lib/ld-linux-x86-64.so.2 a.out

Solution 2:

.out is an unusual extension. Usually this would normally signify a "trace output" file.

Check your syntax that you are using to compile

e.g.

gcc myfile.c /usr/lib/libsomelibrary.a -o outputfilename

or maybe

g++ myfile.cpp -lm -o outputfilename

You can should examine to see if the executable bit is set on the file

ls -l a.out

or you can just force the executable bit

chmod +x a.out

then you can run your file

./a.out

or simply

a.out

You should also perhaps check that the output file has been written correctly as a binary

i.e.

file a.out

This will report what format the file is - either a script or a binary

You rarely need to execute as root unless you have restricted who should be able to run the executable.

If you have compiled as root (e.g. sudo make), or have a Makefile that installed the executable as root then can I suggest you regain the permission as the user logged in

i.e.

sudo chown fred:fred a.out

i.e. replace "fred" with your user id.

Solution 3:

Just copy the folder to your home folder and it will work. You are probably trying to run it on an external drive or something.