There
are few commands in Linux which can be executed on other commands
To see
how the command is executing and what actually is command is doing
strace ls
An excerpt
of the output,
execve("/bin/ls",
["ls"], [/* 36 vars */]) = 0
brk(0) = 0x8e51000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=61502, ...}) = 0
mmap2(NULL, 61502, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7fb2000
close(3) = 0
open("/lib/librt.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\200\210\213\0004\0\0\0"..., 512) = 512
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fb1000
fstat64(3, {st_mode=S_IFREG|0755, st_size=48156, ...}) = 0
mmap2(0x8b7000, 33324, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x8b7000
mmap2(0x8be000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x7) = 0x8be000
close(3) = 0
open("/lib/libacl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0@2\212\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=25624, ...}) = 0
brk(0) = 0x8e51000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=61502, ...}) = 0
mmap2(NULL, 61502, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7fb2000
close(3) = 0
open("/lib/librt.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\200\210\213\0004\0\0\0"..., 512) = 512
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fb1000
fstat64(3, {st_mode=S_IFREG|0755, st_size=48156, ...}) = 0
mmap2(0x8b7000, 33324, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x8b7000
mmap2(0x8be000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x7) = 0x8be000
close(3) = 0
open("/lib/libacl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0@2\212\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=25624, ...}) = 0
Strace
is to trace system calls and signals
Monitor
activity: We can monitor activity using the watch command ,
watch
–l 3 logName.log
watch
command is used execute a program
periodically, showing output fullscreen. We can pass the time to execute the
command using “-l”
Time : we
can use time command to find how much time the command has taken to execute
Time ls
Whereis: we
can use this to find the location of the command ,
Whereis ls
Whatis: we
can use this command to get information about a command
Whatis ls
Happy learning :-)
