I read online that this mantra translates into "I bow to Shiva, who represents the inner self" and helps the chanter attain realization of the inner self.
Can this mantra also be used as a general prayer for the help and protection of Shiva? For example, can chanting this mantra call on Shiva to reduce a particular source of suffering or ignorance in one's life?
Even without the OM prefixed, the five-lettered mantra " namaha Shivaya" is a Veda mantra.
It is originally found in the Yajurveda. Its among the most popular and powerful Veda mantras along with the GAyatri and the Tryambaka mantras (another Shiva mantra).
Namah Shambhave cha mayobhave cha, namah shankaraya cha mayaskaraya cha, namah shivAya cha shivatarAya cha.
............
Salutation to the source of peace and to the source of delight, salutation to one who creates peace and who creates delight, salutation to the auspicious one (Shiva) and to the more auspicious one (or the paramatman or the absolute).
Mantras from Yajur Veda, Tattriya Samhita 4.5.8
Now, scriptures (the Smritis for example) will say that only those who have GAyatri mantra DikshA can chant the Veda mantras. Others can not. For example:
Manu Smriti 2.172. (He who has not been initiated) should not pronounce (any) Vedic text excepting (those required for) the performance of funeral rites, since he is on a level with a Sudra before his birth from the Veda.
So, if you are a strict follower of scriptures you should not chant it without initiation. But plenty do chant it without doubt.
IMO, it's better to go for simple slokas and stotras instead.
Now, here's an alternative:
As per the great saint Sri Ramana Maharshi everyone can chant the mantra "Arunachala Shiva". I have read that according to him everyone, initiates and non-initiates, can chant this mantra and its also an extremely potent mantra. He says that it is as powerful as the panchAkshari mantra and also note that the word A-ru-na-cha-la is also five-lettered.
You can learn more about it on this page and from their website.
As Per Shiva purana, The Shadakshara mantra (Om Namah Shivaya) can be chanted both with or without having received it from a perceptor.
Though recieving it from a guru is still stated to be better.
~ Shiva Purana, Vayaviya Samhita, Uttara Khanda, Chapter 26
This is a tricky question because this mantra is also Vedic as well as Puranic. But a little careful analysis makes it easy to understand.
The mantra is panchAkshari mantra and not shaDAkshari i.e five syllabled mantra. Hence there is no "om" in the beginning of the mantra. While chanting the vedas, this is not chanted with omkaara.
Om is usually added to mantras to make it more powerful and sacred. It is not a mandatory practice though.
This mantra appears in the Krishna Yajurveda in 8th anuvAka of the famous "chamakam" section.
नमः साेमाय च रुद्राय च नमस्ताम्राय चारुणाय च नमः शड़्गाय च पशुपतये च नम उग्राय च भीमाय च नमाे अग्रेवधाय च दूरेवधाय च नमाे हन्त्रे च हनीयसे च नमाे वृक्ष्यभ्यो हरिकेशेभ्याे नमस्ताराय नमः शंभवे च मयाेभवे च नमः शंकराय च मयस्कराय च नमः शिवाय च शिवतराय च ॥ ८ -१॥
In this prayer there are many words which are also having "namah".
If we see its viniyoga, the rishis here is "aghora".
अस्य श्री रुद्राध्याय प्रश्न महामन्त्रस्य, अघोर ऋषिः, अनुष्टुप् चन्दः, सङ्कर्षण मूर्ति स्वरूपो योஉसावादित्यः परमपुरुषः स एष रुद्रो देवता । नमः शिवायेति बीजम् । शिवतरायेति शक्तिः । महादेवायेति कीलकम् । श्री साम्ब सदाशिव प्रसाद सिद्ध्यर्थे जपे विनियोगः ॥
This mantra also also in the Shukla Yajurveda Samhita.
Here the rishi is ParameshThi.
Further, this mantra is also available in purAnas/agamas where,
As per Linga puranam,
Guhyaadguhyataram saakshaanmoksha Jnaanamanuttamam,
Asya Mantrasya vakshyaami Rishicchandodhi Daivatam/
Beejam Shaktih Swaram varnam sthaanam chaivaaksharam prati,
Vamadevo naama Rishih Panktiscchanda udaatdhrutah/
Devataa Shiva yevaaham Mantrasyaasya varaananey,
Here, the Rishi is Sri vAmadeva and chhandas is pankti.
So, technically the mantra is given to different people at different times. It also appears in Vedas as well as puranas and tantra. It has different rishis when it comes to agama and puranas.
Hence in that way, it is NOT ONLY a Vedic mantra but also puranic mantra.
Further, it also appears in many stotras such as:
नागेन्द्रहाराय त्रिलोचनाय भस्मांगरागाय महेश्वराय।
नित्याय शुद्धाय दिगम्बराय तस्मै ‘न’काराय नम: शिवाय।।
मन्दाकिनी सलिलचन्दनचर्चिताय नन्दीश्वर प्रमथनाथ महेश्वराय।
मन्दारपुष्पबहुपुष्प सुपूजिताय तस्मै ‘म’काराय नम: शिवाय। (shiva panchAkshara stotram)
Hence there is no hard and fast rules with respect to initiation because it is also part of Non Vedic literature as well as stotras which usually does not need initiation.
But it is always the best to get it from a Sadguru.
Skanda purana states that while Initiation is not mandatory, it is recommended to get this mantra from a guru.
If the Mantra oṃ namaḥ śivāya is fixed in the heart, of what avail are many other Mantras, many of the holy places, penances and sacrifices to him?
As long as embodied beings do not utter this Mantra even once, so long do they move round and round in the terrible mundane world infested with miseries.
This six-syllabled Mantra is the supreme king of the kings of all the Mantras, the crest-jewel of all the Vedāntas, the storehouse of all spiritual knowledge.
This Mantra of six-syllables is the illuminating lamp on the path of salvation, the submarine-fire unto the ocean of ignorance, the forest-fire of great woods of heinous sins.
Hence this five-lettered Mantra is declared as the bestower of everything. It may be practised (muttered) even by women, Śūdras and men of mixed caste and nativity desirous of salvation.
21. There is neither special initiation in regard to this Mantra nor Homa; neither consecration nor water-libation (or other means of propitiation); neither a special occasion nor special process of instruction. This Mantra is ever pure.
22. The set of two letters ‘śi va’ accompanied by the word indicating obeisance (i.e. śivāya namaḥ) is capable of destroying great sins and granting salvation.
23. What wonder is there if this Mantra taught by a good preceptor and repeated in a sacred place accords immediately every supernatural power desired (by the devotee)!
24. Hence this leader of Mantras should be acquired after resorting to an excellent preceptor, and should be repeatedly muttered in holy places. It gives inordinate powers instantly.
~ Skanda purana Brāhma-khaṇḍa Brāhmottara-khaṇḍa Chapter 1
